httpcore.c

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/*
 * Copyright (C) 2015 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );

/**
 * @file
 *
 * Hyper Text Transfer Protocol (HTTP) core functionality
 *
 */

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <strings.h>
#include <byteswap.h>
#include <errno.h>
#include <ctype.h>
#include <assert.h>
#include <ipxe/uri.h>
#include <ipxe/refcnt.h>
#include <ipxe/iobuf.h>
#include <ipxe/xfer.h>
#include <ipxe/open.h>
#include <ipxe/process.h>
#include <ipxe/retry.h>
#include <ipxe/timer.h>
#include <ipxe/linebuf.h>
#include <ipxe/xferbuf.h>
#include <ipxe/blockdev.h>
#include <ipxe/acpi.h>
#include <ipxe/version.h>
#include <ipxe/params.h>
#include <ipxe/profile.h>
#include <ipxe/vsprintf.h>
#include <ipxe/errortab.h>
#include <ipxe/efi/efi_path.h>
#include <ipxe/http.h>

/* Disambiguate the various error causes */
#define EACCES_401 __einfo_error ( EINFO_EACCES_401 )
#define EINFO_EACCES_401 \
        __einfo_uniqify ( EINFO_EACCES, 0x01, "HTTP 401 Unauthorized" )
#define EINVAL_STATUS __einfo_error ( EINFO_EINVAL_STATUS )
#define EINFO_EINVAL_STATUS \
        __einfo_uniqify ( EINFO_EINVAL, 0x01, "Invalid status line" )
#define EINVAL_HEADER __einfo_error ( EINFO_EINVAL_HEADER )
#define EINFO_EINVAL_HEADER \
        __einfo_uniqify ( EINFO_EINVAL, 0x02, "Invalid header" )
#define EINVAL_CONTENT_LENGTH __einfo_error ( EINFO_EINVAL_CONTENT_LENGTH )
#define EINFO_EINVAL_CONTENT_LENGTH \
        __einfo_uniqify ( EINFO_EINVAL, 0x03, "Invalid content length" )
#define EINVAL_CHUNK_LENGTH __einfo_error ( EINFO_EINVAL_CHUNK_LENGTH )
#define EINFO_EINVAL_CHUNK_LENGTH \
        __einfo_uniqify ( EINFO_EINVAL, 0x04, "Invalid chunk length" )
#define EIO_OTHER __einfo_error ( EINFO_EIO_OTHER )
#define EINFO_EIO_OTHER \
        __einfo_uniqify ( EINFO_EIO, 0x01, "Unrecognised HTTP response code" )
#define EIO_CONTENT_LENGTH __einfo_error ( EINFO_EIO_CONTENT_LENGTH )
#define EINFO_EIO_CONTENT_LENGTH \
        __einfo_uniqify ( EINFO_EIO, 0x02, "Content length mismatch" )
#define EIO_4XX __einfo_error ( EINFO_EIO_4XX )
#define EINFO_EIO_4XX \
        __einfo_uniqify ( EINFO_EIO, 0x04, "HTTP 4xx Client Error" )
#define EIO_5XX __einfo_error ( EINFO_EIO_5XX )
#define EINFO_EIO_5XX \
        __einfo_uniqify ( EINFO_EIO, 0x05, "HTTP 5xx Server Error" )
#define ENOENT_404 __einfo_error ( EINFO_ENOENT_404 )
#define EINFO_ENOENT_404 \
        __einfo_uniqify ( EINFO_ENOENT, 0x01, "Not found" )
#define ENOTSUP_CONNECTION __einfo_error ( EINFO_ENOTSUP_CONNECTION )
#define EINFO_ENOTSUP_CONNECTION \
        __einfo_uniqify ( EINFO_ENOTSUP, 0x01, "Unsupported connection header" )
#define ENOTSUP_TRANSFER __einfo_error ( EINFO_ENOTSUP_TRANSFER )
#define EINFO_ENOTSUP_TRANSFER \
        __einfo_uniqify ( EINFO_ENOTSUP, 0x02, "Unsupported transfer encoding" )
#define EPERM_403 __einfo_error ( EINFO_EPERM_403 )
#define EINFO_EPERM_403 \
        __einfo_uniqify ( EINFO_EPERM, 0x01, "HTTP 403 Forbidden" )
#define EPROTO_UNSOLICITED __einfo_error ( EINFO_EPROTO_UNSOLICITED )
#define EINFO_EPROTO_UNSOLICITED \
        __einfo_uniqify ( EINFO_EPROTO, 0x01, "Unsolicited data" )

/** Retry delay used when we cannot understand the Retry-After header */
#define HTTP_RETRY_SECONDS 5

/** Idle connection watchdog timeout */
#define HTTP_WATCHDOG_SECONDS 120

/** Receive profiler */
static struct profiler http_rx_profiler __profiler = { .name = "http.rx" };

/** Data transfer profiler */
static struct profiler http_xfer_profiler __profiler = { .name = "http.xfer" };

/** Human-readable error messages */
struct errortab http_errors[] __errortab = {
        __einfo_errortab ( EINFO_ENOENT_404 ),
        __einfo_errortab ( EINFO_EIO_4XX ),
        __einfo_errortab ( EINFO_EIO_5XX ),
};

static struct http_state http_request;
static struct http_state http_headers;
static struct http_state http_trailers;
static struct http_transfer_encoding http_transfer_identity;

/******************************************************************************
 *
 * Methods
 *
 ******************************************************************************
 */

/** HTTP HEAD method */
struct http_method http_head = {
        .name = "HEAD",
};

/** HTTP GET method */
struct http_method http_get = {
        .name = "GET",
};

/** HTTP POST method */
struct http_method http_post = {
        .name = "POST",
};

/******************************************************************************
 *
 * Utility functions
 *
 ******************************************************************************
 */

/**
 * Handle received HTTP line-buffered data
 *
 * @v http              HTTP transaction
 * @v iobuf             I/O buffer
 * @v linebuf           Line buffer
 * @ret rc              Return status code
 */
static int http_rx_linebuf ( struct http_transaction *http,
                             struct io_buffer *iobuf,
                             struct line_buffer *linebuf ) {
        int consumed;
        int rc;

        /* Buffer received line */
        consumed = line_buffer ( linebuf, iobuf->data, iob_len ( iobuf ) );
        if ( consumed < 0 ) {
                rc = consumed;
                DBGC ( http, "HTTP %p could not buffer line: %s\n",
                       http, strerror ( rc ) );
                return rc;
        }

        /* Consume line */
        iob_pull ( iobuf, consumed );

        return 0;
}

/**
 * Get HTTP response token
 *
 * @v line              Line position
 * @v value             Token value to fill in (if any)
 * @ret token           Token, or NULL
 */
char * http_token ( char **line, char **value ) {
        char *token;
        char quote = '\0';
        char c;

        /* Avoid returning uninitialised data */
        if ( value )
                *value = NULL;

        /* Skip any initial whitespace or commas */
        while ( ( isspace ( **line ) ) || ( **line == ',' ) )
                (*line)++;

        /* Check for end of line and record token position */
        if ( ! **line )
                return NULL;
        token = *line;

        /* Scan for end of token */
        while ( ( c = **line ) ) {

                /* Terminate if we hit an unquoted whitespace or comma */
                if ( ( isspace ( c ) || ( c == ',' ) ) && ! quote )
                        break;

                /* Terminate if we hit a closing quote */
                if ( c == quote )
                        break;

                /* Check for value separator */
                if ( value && ( ! *value ) && ( c == '=' ) ) {

                        /* Terminate key portion of token */
                        *((*line)++) = '\0';

                        /* Check for quote character */
                        c = **line;
                        if ( ( c == '"' ) || ( c == '\'' ) ) {
                                quote = c;
                                (*line)++;
                        }

                        /* Record value portion of token */
                        *value = *line;

                } else {

                        /* Move to next character */
                        (*line)++;
                }
        }

        /* Terminate token, if applicable */
        if ( c )
                *((*line)++) = '\0';

        return token;
}

/******************************************************************************
 *
 * Transactions
 *
 ******************************************************************************
 */

/**
 * Free HTTP transaction
 *
 * @v refcnt            Reference count
 */
static void http_free ( struct refcnt *refcnt ) {
        struct http_transaction *http =
                container_of ( refcnt, struct http_transaction, refcnt );

        empty_line_buffer ( &http->response.headers );
        empty_line_buffer ( &http->linebuf );
        uri_put ( http->uri );
        free ( http );
}

/**
 * Close HTTP transaction
 *
 * @v http              HTTP transaction
 * @v rc                Reason for close
 */
static void http_close ( struct http_transaction *http, int rc ) {

        /* Stop process */
        process_del ( &http->process );

        /* Stop timers */
        stop_timer ( &http->retry );
        stop_timer ( &http->watchdog );

        /* Close all interfaces */
        intfs_shutdown ( rc, &http->conn, &http->transfer, &http->content,
                         &http->xfer, NULL );
}

/**
 * Close HTTP transaction with error (even if none specified)
 *
 * @v http              HTTP transaction
 * @v rc                Reason for close
 */
static void http_close_error ( struct http_transaction *http, int rc ) {

        /* Treat any close as an error */
        http_close ( http, ( rc ? rc : -EPIPE ) );
}

/**
 * Hold off HTTP idle connection watchdog timer
 *
 * @v http              HTTP transaction
 */
static inline void http_watchdog ( struct http_transaction *http ) {

        /* (Re)start watchdog timer */
        start_timer_fixed ( &http->watchdog,
                            ( HTTP_WATCHDOG_SECONDS * TICKS_PER_SEC ) );
}

/**
 * Reopen stale HTTP connection
 *
 * @v http              HTTP transaction
 */
static void http_reopen ( struct http_transaction *http ) {
        int rc;

        /* Close existing connection */
        intf_restart ( &http->conn, -ECANCELED );

        /* Reopen connection */
        if ( ( rc = http_connect ( &http->conn, http->uri ) ) != 0 ) {
                DBGC ( http, "HTTP %p could not reconnect: %s\n",
                       http, strerror ( rc ) );
                goto err_connect;
        }

        /* Reset state */
        http->state = &http_request;

        /* Restart idle connection watchdog timer */
        http_watchdog ( http );

        /* Reschedule transmission process */
        process_add ( &http->process );

        return;

 err_connect:
        http_close ( http, rc );
}

/**
 * Handle connection retry timer expiry
 *
 * @v retry             Retry timer
 * @v over              Failure indicator
 */
static void http_retry_expired ( struct retry_timer *retry,
                                 int over __unused ) {
        struct http_transaction *http =
                container_of ( retry, struct http_transaction, retry );

        /* Reopen connection */
        http_reopen ( http );
}

/**
 * Handle idle connection watchdog timer expiry
 *
 * @v watchdog          Idle connection watchdog timer
 * @v over              Failure indicator
 */
static void http_watchdog_expired ( struct retry_timer *watchdog,
                                    int over __unused ) {
        struct http_transaction *http =
                container_of ( watchdog, struct http_transaction, watchdog );

        /* Abort connection */
        DBGC ( http, "HTTP %p aborting idle connection\n", http );
        http_close ( http, -ETIMEDOUT );
}

/**
 * HTTP transmit process
 *
 * @v http              HTTP transaction
 */
static void http_step ( struct http_transaction *http ) {
        int rc;

        /* Do nothing if we have nothing to transmit */
        if ( ! http->state->tx )
                return;

        /* Do nothing until connection is ready */
        if ( ! xfer_window ( &http->conn ) )
                return;

        /* Notify data transfer interface that window may have changed */
        xfer_window_changed ( &http->xfer );

        /* Do nothing until data transfer interface is ready */
        if ( ! xfer_window ( &http->xfer ) )
                return;

        /* Transmit data */
        if ( ( rc = http->state->tx ( http ) ) != 0 )
                goto err;

        return;

 err:
        http_close ( http, rc );
}

/**
 * Handle received HTTP data
 *
 * @v http              HTTP transaction
 * @v iobuf             I/O buffer
 * @v meta              Transfer metadata
 * @ret rc              Return status code
 *
 * This function takes ownership of the I/O buffer.
 */
static int http_conn_deliver ( struct http_transaction *http,
                               struct io_buffer *iobuf,
                               struct xfer_metadata *meta __unused ) {
        int rc;

        /* Handle received data */
        profile_start ( &http_rx_profiler );
        while ( iobuf && iob_len ( iobuf ) ) {

                /* Sanity check */
                if ( ( ! http->state ) || ( ! http->state->rx ) ) {
                        DBGC ( http, "HTTP %p unexpected data\n", http );
                        rc = -EPROTO_UNSOLICITED;
                        goto err;
                }

                /* Receive (some) data */
                if ( ( rc = http->state->rx ( http, &iobuf ) ) != 0 )
                        goto err;
        }

        /* Free I/O buffer, if applicable */
        free_iob ( iobuf );

        profile_stop ( &http_rx_profiler );
        return 0;

 err:
        free_iob ( iobuf );
        http_close ( http, rc );
        return rc;
}

/**
 * Handle server connection close
 *
 * @v http              HTTP transaction
 * @v rc                Reason for close
 */
static void http_conn_close ( struct http_transaction *http, int rc ) {

        /* Sanity checks */
        assert ( http->state != NULL );
        assert ( http->state->close != NULL );

        /* Restart server connection interface */
        intf_restart ( &http->conn, rc );

        /* Hand off to state-specific method */
        http->state->close ( http, rc );
}

/**
 * Handle received content-decoded data
 *
 * @v http              HTTP transaction
 * @v iobuf             I/O buffer
 * @v meta              Data transfer metadata
 */
static int http_content_deliver ( struct http_transaction *http,
                                  struct io_buffer *iobuf,
                                  struct xfer_metadata *meta ) {
        int rc;

        /* Ignore content if this is anything other than a successful
         * transfer.
         */
        if ( http->response.rc != 0 ) {
                free_iob ( iobuf );
                return 0;
        }

        /* Hold off idle connection watchdog timer */
        http_watchdog ( http );

        /* Deliver to data transfer interface */
        profile_start ( &http_xfer_profiler );
        if ( ( rc = xfer_deliver ( &http->xfer, iob_disown ( iobuf ),
                                   meta ) ) != 0 )
                return rc;
        profile_stop ( &http_xfer_profiler );

        return 0;
}

/**
 * Get underlying data transfer buffer
 *
 * @v http              HTTP transaction
 * @ret xferbuf         Data transfer buffer, or NULL on error
 */
static struct xfer_buffer *
http_content_buffer ( struct http_transaction *http ) {

        /* Deny access to the data transfer buffer if this is anything
         * other than a successful transfer.
         */
        if ( http->response.rc != 0 )
                return NULL;

        /* Hand off to data transfer interface */
        return xfer_buffer ( &http->xfer );
}

/**
 * Read from block device (when HTTP block device support is not present)
 *
 * @v http              HTTP transaction
 * @v data              Data interface
 * @v lba               Starting logical block address
 * @v count             Number of logical blocks
 * @v buffer            Data buffer
 * @v len               Length of data buffer
 * @ret rc              Return status code
 */
__weak int http_block_read ( struct http_transaction *http __unused,
                             struct interface *data __unused,
                             uint64_t lba __unused, unsigned int count __unused,
                             void *buffer __unused, size_t len __unused ) {

        return -ENOTSUP;
}

/**
 * Read block device capacity (when HTTP block device support is not present)
 *
 * @v control           Control interface
 * @v data              Data interface
 * @ret rc              Return status code
 */
__weak int http_block_read_capacity ( struct http_transaction *http __unused,
                                      struct interface *data __unused ) {

        return -ENOTSUP;
}

/**
 * Describe as an EFI device path
 *
 * @v http              HTTP transaction
 * @ret path            EFI device path, or NULL on error
 */
static EFI_DEVICE_PATH_PROTOCOL *
http_efi_describe ( struct http_transaction *http ) {

        return efi_uri_path ( http->uri );
}

/** HTTP data transfer interface operations */
static struct interface_operation http_xfer_operations[] = {
        INTF_OP ( block_read, struct http_transaction *, http_block_read ),
        INTF_OP ( block_read_capacity, struct http_transaction *,
                  http_block_read_capacity ),
        INTF_OP ( xfer_window_changed, struct http_transaction *, http_step ),
        INTF_OP ( intf_close, struct http_transaction *, http_close ),
        EFI_INTF_OP ( efi_describe, struct http_transaction *,
                      http_efi_describe ),
};

/** HTTP data transfer interface descriptor */
static struct interface_descriptor http_xfer_desc =
        INTF_DESC_PASSTHRU ( struct http_transaction, xfer,
                             http_xfer_operations, content );

/** HTTP content-decoded interface operations */
static struct interface_operation http_content_operations[] = {
        INTF_OP ( xfer_deliver, struct http_transaction *,
                  http_content_deliver ),
        INTF_OP ( xfer_buffer, struct http_transaction *, http_content_buffer ),
        INTF_OP ( intf_close, struct http_transaction *, http_close ),
};

/** HTTP content-decoded interface descriptor */
static struct interface_descriptor http_content_desc =
        INTF_DESC_PASSTHRU ( struct http_transaction, content,
                             http_content_operations, xfer );

/** HTTP transfer-decoded interface operations */
static struct interface_operation http_transfer_operations[] = {
        INTF_OP ( intf_close, struct http_transaction *, http_close ),
};

/** HTTP transfer-decoded interface descriptor */
static struct interface_descriptor http_transfer_desc =
        INTF_DESC_PASSTHRU ( struct http_transaction, transfer,
                             http_transfer_operations, conn );

/** HTTP server connection interface operations */
static struct interface_operation http_conn_operations[] = {
        INTF_OP ( xfer_deliver, struct http_transaction *, http_conn_deliver ),
        INTF_OP ( xfer_window_changed, struct http_transaction *, http_step ),
        INTF_OP ( pool_reopen, struct http_transaction *, http_reopen ),
        INTF_OP ( intf_close, struct http_transaction *, http_conn_close ),
};

/** HTTP server connection interface descriptor */
static struct interface_descriptor http_conn_desc =
        INTF_DESC_PASSTHRU ( struct http_transaction, conn,
                             http_conn_operations, transfer );

/** HTTP process descriptor */
static struct process_descriptor http_process_desc =
        PROC_DESC_ONCE ( struct http_transaction, process, http_step );

/**
 * Open HTTP transaction
 *
 * @v xfer              Data transfer interface
 * @v method            Request method
 * @v uri               Request URI
 * @v range             Content range (if any)
 * @v content           Request content (if any)
 * @ret rc              Return status code
 */
int http_open ( struct interface *xfer, struct http_method *method,
                struct uri *uri, struct http_request_range *range,
                struct http_request_content *content ) {
        struct http_transaction *http;
        struct uri request_uri;
        struct uri request_host;
        size_t request_uri_len;
        size_t request_host_len;
        size_t content_len;
        char *request_uri_string;
        char *request_host_string;
        void *content_data;
        int rc;

        /* Calculate request URI length */
        memset ( &request_uri, 0, sizeof ( request_uri ) );
        request_uri.epath = ( uri->epath ? uri->epath : "/" );
        request_uri.equery = uri->equery;
        request_uri_len =
                ( format_uri ( &request_uri, NULL, 0 ) + 1 /* NUL */);

        /* Calculate host name length */
        memset ( &request_host, 0, sizeof ( request_host ) );
        request_host.host = uri->host;
        request_host.port = uri->port;
        request_host_len =
                ( format_uri ( &request_host, NULL, 0 ) + 1 /* NUL */ );

        /* Calculate request content length */
        content_len = ( content ? content->len : 0 );

        /* Allocate and initialise structure */
        http = zalloc ( sizeof ( *http ) + request_uri_len + request_host_len +
                        content_len );
        if ( ! http ) {
                rc = -ENOMEM;
                goto err_alloc;
        }
        request_uri_string = ( ( ( void * ) http ) + sizeof ( *http ) );
        request_host_string = ( request_uri_string + request_uri_len );
        content_data = ( request_host_string + request_host_len );
        format_uri ( &request_uri, request_uri_string, request_uri_len );
        format_uri ( &request_host, request_host_string, request_host_len );
        ref_init ( &http->refcnt, http_free );
        intf_init ( &http->xfer, &http_xfer_desc, &http->refcnt );
        intf_init ( &http->content, &http_content_desc, &http->refcnt );
        intf_init ( &http->transfer, &http_transfer_desc, &http->refcnt );
        intf_init ( &http->conn, &http_conn_desc, &http->refcnt );
        intf_plug_plug ( &http->transfer, &http->content );
        process_init ( &http->process, &http_process_desc, &http->refcnt );
        timer_init ( &http->retry, http_retry_expired, &http->refcnt );
        timer_init ( &http->watchdog, http_watchdog_expired, &http->refcnt );
        http->uri = uri_get ( uri );
        http->request.method = method;
        http->request.uri = request_uri_string;
        http->request.host = request_host_string;
        if ( range ) {
                memcpy ( &http->request.range, range,
                         sizeof ( http->request.range ) );
        }
        if ( content ) {
                http->request.content.type = content->type;
                http->request.content.data = content_data;
                http->request.content.len = content_len;
                memcpy ( content_data, content->data, content_len );
        }
        http->state = &http_request;
        DBGC2 ( http, "HTTP %p %s://%s%s\n", http, http->uri->scheme,
                http->request.host, http->request.uri );

        /* Open connection */
        if ( ( rc = http_connect ( &http->conn, uri ) ) != 0 ) {
                DBGC ( http, "HTTP %p could not connect: %s\n",
                       http, strerror ( rc ) );
                goto err_connect;
        }

        /* Start watchdog timer */
        http_watchdog ( http );

        /* Attach to parent interface, mortalise self, and return */
        intf_plug_plug ( &http->xfer, xfer );
        ref_put ( &http->refcnt );
        return 0;

 err_connect:
        http_close ( http, rc );
        ref_put ( &http->refcnt );
 err_alloc:
        return rc;
}

/**
 * Redirect HTTP transaction
 *
 * @v http              HTTP transaction
 * @v location          New location
 * @ret rc              Return status code
 */
static int http_redirect ( struct http_transaction *http,
                           const char *location ) {
        struct uri *location_uri;
        struct uri *resolved_uri;
        int rc;

        DBGC2 ( http, "HTTP %p redirecting to \"%s\"\n", http, location );

        /* Parse location URI */
        location_uri = parse_uri ( location );
        if ( ! location_uri ) {
                rc = -ENOMEM;
                goto err_parse_uri;
        }

        /* Resolve as relative to original URI */
        resolved_uri = resolve_uri ( http->uri, location_uri );
        if ( ! resolved_uri ) {
                rc = -ENOMEM;
                goto err_resolve_uri;
        }

        /* Redirect to new URI */
        if ( ( rc = xfer_redirect ( &http->xfer, LOCATION_URI,
                                    resolved_uri ) ) != 0 ) {
                DBGC ( http, "HTTP %p could not redirect: %s\n",
                       http, strerror ( rc ) );
                goto err_redirect;
        }

 err_redirect:
        uri_put ( resolved_uri );
 err_resolve_uri:
        uri_put ( location_uri );
 err_parse_uri:
        return rc;
}

/**
 * Handle successful transfer completion
 *
 * @v http              HTTP transaction
 * @ret rc              Return status code
 */
static int http_transfer_complete ( struct http_transaction *http ) {
        struct http_authentication *auth;
        const char *location;
        int rc;

        /* Keep connection alive if applicable */
        if ( http->response.flags & HTTP_RESPONSE_KEEPALIVE )
                pool_recycle ( &http->conn );

        /* Restart server connection interface */
        intf_restart ( &http->conn, 0 );

        /* No more data is expected */
        http->state = NULL;

        /* If transaction is successful, then close the
         * transfer-decoded interface.  The content encoding may
         * choose whether or not to immediately terminate the
         * transaction.
         */
        if ( http->response.rc == 0 ) {
                intf_shutdown ( &http->transfer, 0 );
                return 0;
        }

        /* Perform redirection, if applicable */
        if ( ( location = http->response.location ) ) {
                if ( ( rc = http_redirect ( http, location ) ) != 0 )
                        return rc;
                http_close ( http, 0 );
                return 0;
        }

        /* Fail unless a retry is permitted */
        if ( ! ( http->response.flags & HTTP_RESPONSE_RETRY ) )
                return http->response.rc;

        /* Perform authentication, if applicable */
        if ( ( auth = http->response.auth.auth ) ) {
                http->request.auth.auth = auth;
                DBGC2 ( http, "HTTP %p performing %s authentication\n",
                        http, auth->name );
                if ( ( rc = auth->authenticate ( http ) ) != 0 ) {
                        DBGC ( http, "HTTP %p could not authenticate: %s\n",
                               http, strerror ( rc ) );
                        return rc;
                }
        }

        /* Restart content decoding interfaces */
        intfs_restart ( http->response.rc, &http->content, &http->transfer,
                        NULL );
        intf_plug_plug ( &http->transfer, &http->content );
        http->len = 0;
        assert ( http->remaining == 0 );

        /* Retry immediately if applicable.  We cannot rely on an
         * immediate timer expiry, since certain Microsoft-designed
         * HTTP extensions such as NTLM break the fundamentally
         * stateless nature of HTTP and rely on the same connection
         * being reused for authentication.  See RFC7230 section 2.3
         * for further details.
         */
        if ( ! http->response.retry_after ) {
                http_reopen ( http );
                return 0;
        }

        /* Start timer to initiate retry */
        DBGC2 ( http, "HTTP %p retrying after %d seconds\n",
                http, http->response.retry_after );
        start_timer_fixed ( &http->retry,
                            ( http->response.retry_after * TICKS_PER_SEC ) );
        stop_timer ( &http->watchdog );
        return 0;
}

/******************************************************************************
 *
 * Requests
 *
 ******************************************************************************
 */

/**
 * Construct HTTP request headers
 *
 * @v http              HTTP transaction
 * @v buf               Buffer
 * @v len               Length of buffer
 * @ret len             Length, or negative error
 */
static int http_format_headers ( struct http_transaction *http, char *buf,
                                 size_t len ) {
        struct parameters *params = http->uri->params;
        struct http_request_header *header;
        struct parameter *param;
        size_t used;
        size_t remaining;
        char *line;
        int value_len;
        int rc;

        /* Construct request line */
        used = ssnprintf ( buf, len, "%s %s HTTP/1.1",
                           http->request.method->name, http->request.uri );
        if ( used < len )
                DBGC2 ( http, "HTTP %p TX %s\n", http, buf );
        used += ssnprintf ( ( buf + used ), ( len - used ), "\r\n" );

        /* Construct all fixed headers */
        for_each_table_entry ( header, HTTP_REQUEST_HEADERS ) {

                /* Determine header value length */
                value_len = header->format ( http, NULL, 0 );
                if ( value_len < 0 ) {
                        rc = value_len;
                        return rc;
                }

                /* Skip zero-length headers */
                if ( ! value_len )
                        continue;

                /* Construct header */
                line = ( buf + used );
                used += ssnprintf ( ( buf + used ), ( len - used ), "%s: ",
                                    header->name );
                remaining = ( ( used < len ) ? ( len - used ) : 0 );
                used += header->format ( http, ( buf + used ), remaining );
                if ( used < len )
                        DBGC2 ( http, "HTTP %p TX %s\n", http, line );
                used += ssnprintf ( ( buf + used ), ( len - used ), "\r\n" );
        }

        /* Construct parameter headers, if any */
        if ( params ) {

                /* Construct all parameter headers */
                for_each_param ( param, params ) {

                        /* Skip non-header parameters */
                        if ( ! ( param->flags & PARAMETER_HEADER ) )
                                continue;

                        /* Add parameter */
                        used += ssnprintf ( ( buf + used ), ( len - used ),
                                            "%s: %s\r\n", param->key,
                                            param->value );
                }
        }

        /* Construct terminating newline */
        used += ssnprintf ( ( buf + used ), ( len - used ), "\r\n" );

        return used;
}

/**
 * Construct HTTP "Host" header
 *
 * @v http              HTTP transaction
 * @v buf               Buffer
 * @v len               Length of buffer
 * @ret len             Length of header value, or negative error
 */
static int http_format_host ( struct http_transaction *http, char *buf,
                              size_t len ) {

        /* Construct host URI */
        return snprintf ( buf, len, "%s", http->request.host );
}

/** HTTP "Host" header "*/
struct http_request_header http_request_host __http_request_header = {
        .name = "Host",
        .format = http_format_host,
};

/**
 * Construct HTTP "User-Agent" header
 *
 * @v http              HTTP transaction
 * @v buf               Buffer
 * @v len               Length of buffer
 * @ret len             Length of header value, or negative error
 */
static int http_format_user_agent ( struct http_transaction *http __unused,
                                    char *buf, size_t len ) {

        /* Construct user agent */
        return snprintf ( buf, len, "iPXE/%s", product_version );
}

/** HTTP "User-Agent" header */
struct http_request_header http_request_user_agent __http_request_header = {
        .name = "User-Agent",
        .format = http_format_user_agent,
};

/**
 * Construct HTTP "Connection" header
 *
 * @v http              HTTP transaction
 * @v buf               Buffer
 * @v len               Length of buffer
 * @ret len             Length of header value, or negative error
 */
static int http_format_connection ( struct http_transaction *http __unused,
                                    char *buf, size_t len ) {

        /* Always request keep-alive */
        return snprintf ( buf, len, "keep-alive" );
}

/** HTTP "Connection" header */
struct http_request_header http_request_connection __http_request_header = {
        .name = "Connection",
        .format = http_format_connection,
};

/**
 * Construct HTTP "Range" header
 *
 * @v http              HTTP transaction
 * @v buf               Buffer
 * @v len               Length of buffer
 * @ret len             Length of header value, or negative error
 */
static int http_format_range ( struct http_transaction *http,
                               char *buf, size_t len ) {

        /* Construct range, if applicable */
        if ( http->request.range.len ) {
                return snprintf ( buf, len, "bytes=%zd-%zd",
                                  http->request.range.start,
                                  ( http->request.range.start +
                                    http->request.range.len - 1 ) );
        } else {
                return 0;
        }
}

/** HTTP "Range" header */
struct http_request_header http_request_range __http_request_header = {
        .name = "Range",
        .format = http_format_range,
};

/**
 * Construct HTTP "Content-Type" header
 *
 * @v http              HTTP transaction
 * @v buf               Buffer
 * @v len               Length of buffer
 * @ret len             Length of header value, or negative error
 */
static int http_format_content_type ( struct http_transaction *http,
                                      char *buf, size_t len ) {

        /* Construct content type, if applicable */
        if ( http->request.content.type ) {
                return snprintf ( buf, len, "%s", http->request.content.type );
        } else {
                return 0;
        }
}

/** HTTP "Content-Type" header */
struct http_request_header http_request_content_type __http_request_header = {
        .name = "Content-Type",
        .format = http_format_content_type,
};

/**
 * Construct HTTP "Content-Length" header
 *
 * @v http              HTTP transaction
 * @v buf               Buffer
 * @v len               Length of buffer
 * @ret len             Length of header value, or negative error
 */
static int http_format_content_length ( struct http_transaction *http,
                                        char *buf, size_t len ) {

        /* Construct content length, if applicable */
        if ( http->request.content.len ) {
                return snprintf ( buf, len, "%zd", http->request.content.len );
        } else {
                return 0;
        }
}

/** HTTP "Content-Length" header */
struct http_request_header http_request_content_length __http_request_header = {
        .name = "Content-Length",
        .format = http_format_content_length,
};

/**
 * Construct HTTP "Accept-Encoding" header
 *
 * @v http              HTTP transaction
 * @v buf               Buffer
 * @v len               Length of buffer
 * @ret len             Length of header value, or negative error
 */
static int http_format_accept_encoding ( struct http_transaction *http,
                                         char *buf, size_t len ) {
        struct http_content_encoding *encoding;
        const char *sep = "";
        size_t used = 0;

        /* Construct list of content encodings */
        for_each_table_entry ( encoding, HTTP_CONTENT_ENCODINGS ) {
                if ( encoding->supported && ( ! encoding->supported ( http ) ) )
                        continue;
                used += ssnprintf ( ( buf + used ), ( len - used ),
                                    "%s%s", sep, encoding->name );
                sep = ", ";
        }

        return used;
}

/** HTTP "Accept-Encoding" header */
struct http_request_header http_request_accept_encoding __http_request_header ={
        .name = "Accept-Encoding",
        .format = http_format_accept_encoding,
};

/**
 * Transmit request
 *
 * @v http              HTTP transaction
 * @ret rc              Return status code
 */
static int http_tx_request ( struct http_transaction *http ) {
        struct io_buffer *iobuf;
        int len;
        int check_len;
        int rc;

        /* Calculate request length */
        len = http_format_headers ( http, NULL, 0 );
        if ( len < 0 ) {
                rc = len;
                DBGC ( http, "HTTP %p could not construct request: %s\n",
                       http, strerror ( rc ) );
                goto err_len;
        }

        /* Allocate I/O buffer */
        iobuf = xfer_alloc_iob ( &http->conn, ( len + 1 /* NUL */ +
                                                http->request.content.len ) );
        if ( ! iobuf ) {
                rc = -ENOMEM;
                goto err_alloc;
        }

        /* Construct request */
        check_len = http_format_headers ( http, iob_put ( iobuf, len ),
                                          ( len + 1 /* NUL */ ) );
        assert ( check_len == len );
        memcpy ( iob_put ( iobuf, http->request.content.len ),
                 http->request.content.data, http->request.content.len );

        /* Deliver request */
        if ( ( rc = xfer_deliver_iob ( &http->conn,
                                       iob_disown ( iobuf ) ) ) != 0 ) {
                DBGC ( http, "HTTP %p could not deliver request: %s\n",
                       http, strerror ( rc ) );
                goto err_deliver;
        }

        /* Clear any previous response */
        empty_line_buffer ( &http->response.headers );
        memset ( &http->response, 0, sizeof ( http->response ) );

        /* Move to response headers state */
        http->state = &http_headers;

        return 0;

 err_deliver:
        free_iob ( iobuf );
 err_alloc:
 err_len:
        return rc;
}

/** HTTP request state */
static struct http_state http_request = {
        .tx = http_tx_request,
        .close = http_close_error,
};

/******************************************************************************
 *
 * Response headers
 *
 ******************************************************************************
 */

/**
 * Parse HTTP status line
 *
 * @v http              HTTP transaction
 * @v line              Status line
 * @ret rc              Return status code
 */
static int http_parse_status ( struct http_transaction *http, char *line ) {
        char *endp;
        char *version;
        char *vernum;
        char *status;
        int response_rc;

        DBGC2 ( http, "HTTP %p RX %s\n", http, line );

        /* Parse HTTP version */
        version = http_token ( &line, NULL );
        if ( ( ! version ) || ( strncmp ( version, "HTTP/", 5 ) != 0 ) ) {
                DBGC ( http, "HTTP %p malformed version \"%s\"\n", http, line );
                return -EINVAL_STATUS;
        }

        /* Keepalive is enabled by default for anything newer than HTTP/1.0 */
        vernum = ( version + 5 /* "HTTP/" (presence already checked) */ );
        if ( vernum[0] == '0' ) {
                /* HTTP/0.x : keepalive not enabled by default */
        } else if ( strncmp ( vernum, "1.0", 3 ) == 0 ) {
                /* HTTP/1.0 : keepalive not enabled by default */
        } else {
                /* HTTP/1.1 or newer: keepalive enabled by default */
                http->response.flags |= HTTP_RESPONSE_KEEPALIVE;
        }

        /* Parse status code */
        status = line;
        http->response.status = strtoul ( status, &endp, 10 );
        if ( *endp != ' ' ) {
                DBGC ( http, "HTTP %p malformed status code \"%s\"\n",
                       http, status );
                return -EINVAL_STATUS;
        }

        /* Convert HTTP status code to iPXE return status code */
        if ( status[0] == '2' ) {
                /* 2xx Success */
                response_rc = 0;
        } else if ( status[0] == '3' ) {
                /* 3xx Redirection */
                response_rc = -EXDEV;
        } else if ( http->response.status == 401 ) {
                /* 401 Unauthorized */
                response_rc = -EACCES_401;
        } else if ( http->response.status == 403 ) {
                /* 403 Forbidden */
                response_rc = -EPERM_403;
        } else if ( http->response.status == 404 ) {
                /* 404 Not Found */
                response_rc = -ENOENT_404;
        } else if ( status[0] == '4' ) {
                /* 4xx Client Error (not already specified) */
                response_rc = -EIO_4XX;
        } else if ( status[0] == '5' ) {
                /* 5xx Server Error */
                response_rc = -EIO_5XX;
        } else {
                /* Unrecognised */
                response_rc = -EIO_OTHER;
        }
        http->response.rc = response_rc;
        if ( response_rc )
                DBGC ( http, "HTTP %p status %s\n", http, status );

        return 0;
}

/**
 * Parse HTTP header
 *
 * @v http              HTTP transaction
 * @v line              Header line
 * @ret rc              Return status code
 */
static int http_parse_header ( struct http_transaction *http, char *line ) {
        struct http_response_header *header;
        char *name = line;
        char *sep;

        DBGC2 ( http, "HTTP %p RX %s\n", http, line );

        /* Extract header name */
        sep = strchr ( line, ':' );
        if ( ! sep ) {
                DBGC ( http, "HTTP %p malformed header \"%s\"\n", http, line );
                return -EINVAL_HEADER;
        }
        *sep = '\0';

        /* Extract remainder of line */
        line = ( sep + 1 );
        while ( isspace ( *line ) )
                line++;

        /* Process header, if recognised */
        for_each_table_entry ( header, HTTP_RESPONSE_HEADERS ) {
                if ( strcasecmp ( name, header->name ) == 0 )
                        return header->parse ( http, line );
        }

        /* Unrecognised headers should be ignored */
        return 0;
}

/**
 * Parse HTTP response headers
 *
 * @v http              HTTP transaction
 * @ret rc              Return status code
 */
static int http_parse_headers ( struct http_transaction *http ) {
        char *line;
        char *next;
        int rc;

        /* Get status line */
        line = http->response.headers.data;
        assert ( line != NULL );
        next = ( line + strlen ( line ) + 1 /* NUL */ );

        /* Parse status line */
        if ( ( rc = http_parse_status ( http, line ) ) != 0 )
                return rc;

        /* Process header lines */
        while ( 1 ) {

                /* Move to next line */
                line = next;
                next = ( line + strlen ( line ) + 1 /* NUL */ );

                /* Stop on terminating blank line */
                if ( ! line[0] )
                        return 0;

                /* Process header line */
                if ( ( rc = http_parse_header ( http, line ) ) != 0 )
                        return rc;
        }
}

/**
 * Parse HTTP "Location" header
 *
 * @v http              HTTP transaction
 * @v line              Remaining header line
 * @ret rc              Return status code
 */
static int http_parse_location ( struct http_transaction *http, char *line ) {

        /* Store location */
        http->response.location = line;
        return 0;
}

/** HTTP "Location" header */
struct http_response_header http_response_location __http_response_header = {
        .name = "Location",
        .parse = http_parse_location,
};

/**
 * Parse HTTP "Transfer-Encoding" header
 *
 * @v http              HTTP transaction
 * @v line              Remaining header line
 * @ret rc              Return status code
 */
static int http_parse_transfer_encoding ( struct http_transaction *http,
                                          char *line ) {
        struct http_transfer_encoding *encoding;

        /* Check for known transfer encodings */
        for_each_table_entry ( encoding, HTTP_TRANSFER_ENCODINGS ) {
                if ( strcasecmp ( line, encoding->name ) == 0 ) {
                        http->response.transfer.encoding = encoding;
                        return 0;
                }
        }

        DBGC ( http, "HTTP %p unrecognised Transfer-Encoding \"%s\"\n",
               http, line );
        return -ENOTSUP_TRANSFER;
}

/** HTTP "Transfer-Encoding" header */
struct http_response_header
http_response_transfer_encoding __http_response_header = {
        .name = "Transfer-Encoding",
        .parse = http_parse_transfer_encoding,
};

/**
 * Parse HTTP "Connection" header
 *
 * @v http              HTTP transaction
 * @v line              Remaining header line
 * @ret rc              Return status code
 */
static int http_parse_connection ( struct http_transaction *http, char *line ) {
        char *token;

        /* Check for known connection intentions */
        while ( ( token = http_token ( &line, NULL ) ) ) {
                if ( strcasecmp ( token, "keep-alive" ) == 0 )
                        http->response.flags |= HTTP_RESPONSE_KEEPALIVE;
                if ( strcasecmp ( token, "close" ) == 0 )
                        http->response.flags &= ~HTTP_RESPONSE_KEEPALIVE;
        }

        return 0;
}

/** HTTP "Connection" header */
struct http_response_header http_response_connection __http_response_header = {
        .name = "Connection",
        .parse = http_parse_connection,
};

/**
 * Parse HTTP "Content-Length" header
 *
 * @v http              HTTP transaction
 * @v line              Remaining header line
 * @ret rc              Return status code
 */
static int http_parse_content_length ( struct http_transaction *http,
                                       char *line ) {
        char *endp;

        /* Parse length */
        http->response.content.len = strtoul ( line, &endp, 10 );
        if ( *endp != '\0' ) {
                DBGC ( http, "HTTP %p invalid Content-Length \"%s\"\n",
                       http, line );
                return -EINVAL_CONTENT_LENGTH;
        }

        /* Record that we have a content length (since it may be zero) */
        http->response.flags |= HTTP_RESPONSE_CONTENT_LEN;

        return 0;
}

/** HTTP "Content-Length" header */
struct http_response_header
http_response_content_length __http_response_header = {
        .name = "Content-Length",
        .parse = http_parse_content_length,
};

/**
 * Parse HTTP "Content-Encoding" header
 *
 * @v http              HTTP transaction
 * @v line              Remaining header line
 * @ret rc              Return status code
 */
static int http_parse_content_encoding ( struct http_transaction *http,
                                         char *line ) {
        struct http_content_encoding *encoding;

        /* Check for known content encodings */
        for_each_table_entry ( encoding, HTTP_CONTENT_ENCODINGS ) {
                if ( encoding->supported && ( ! encoding->supported ( http ) ) )
                        continue;
                if ( strcasecmp ( line, encoding->name ) == 0 ) {
                        http->response.content.encoding = encoding;
                        return 0;
                }
        }

        /* Some servers (e.g. Apache) have a habit of specifying
         * unwarranted content encodings.  For example, if Apache
         * detects (via /etc/httpd/conf/magic) that a file's contents
         * are gzip-compressed, it will set "Content-Encoding: x-gzip"
         * regardless of the client's Accept-Encoding header.  The
         * only viable way to handle such servers is to treat unknown
         * content encodings as equivalent to "identity".
         */
        DBGC ( http, "HTTP %p unrecognised Content-Encoding \"%s\"\n",
               http, line );
        return 0;
}

/** HTTP "Content-Encoding" header */
struct http_response_header
http_response_content_encoding __http_response_header = {
        .name = "Content-Encoding",
        .parse = http_parse_content_encoding,
};

/**
 * Parse HTTP "Retry-After" header
 *
 * @v http              HTTP transaction
 * @v line              Remaining header line
 * @ret rc              Return status code
 */
static int http_parse_retry_after ( struct http_transaction *http,
                                    char *line ) {
        char *endp;

        /* Try to parse value as a simple number of seconds */
        http->response.retry_after = strtoul ( line, &endp, 10 );
        if ( *endp != '\0' ) {
                /* For any value which is not a simple number of
                 * seconds (e.g. a full HTTP date), just retry after a
                 * fixed delay, since we don't have code able to parse
                 * full HTTP dates.
                 */
                http->response.retry_after = HTTP_RETRY_SECONDS;
                DBGC ( http, "HTTP %p cannot understand Retry-After \"%s\"; "
                       "using %d seconds\n", http, line, HTTP_RETRY_SECONDS );
        }

        /* Allow HTTP request to be retried after specified delay */
        http->response.flags |= HTTP_RESPONSE_RETRY;

        return 0;
}

/** HTTP "Retry-After" header */
struct http_response_header http_response_retry_after __http_response_header = {
        .name = "Retry-After",
        .parse = http_parse_retry_after,
};

/**
 * Handle received HTTP headers
 *
 * @v http              HTTP transaction
 * @v iobuf             I/O buffer (may be claimed)
 * @ret rc              Return status code
 */
static int http_rx_headers ( struct http_transaction *http,
                             struct io_buffer **iobuf ) {
        struct http_transfer_encoding *transfer;
        struct http_content_encoding *content;
        char *line;
        int rc;

        /* Buffer header line */
        if ( ( rc = http_rx_linebuf ( http, *iobuf,
                                      &http->response.headers ) ) != 0 )
                return rc;

        /* Wait until we see the empty line marking end of headers */
        line = buffered_line ( &http->response.headers );
        if ( ( line == NULL ) || ( line[0] != '\0' ) )
                return 0;

        /* Process headers */
        if ( ( rc = http_parse_headers ( http ) ) != 0 )
                return rc;

        /* Initialise content encoding, if applicable */
        if ( ( content = http->response.content.encoding ) &&
             ( ( rc = content->init ( http ) ) != 0 ) ) {
                DBGC ( http, "HTTP %p could not initialise %s content "
                       "encoding: %s\n", http, content->name, strerror ( rc ) );
                return rc;
        }

        /* Presize receive buffer, if we have a content length */
        if ( http->response.content.len ) {
                xfer_seek ( &http->transfer, http->response.content.len );
                xfer_seek ( &http->transfer, 0 );
        }

        /* Complete transfer if this is a HEAD request */
        if ( http->request.method == &http_head ) {
                if ( ( rc = http_transfer_complete ( http ) ) != 0 )
                        return rc;
                return 0;
        }

        /* Default to identity transfer encoding, if none specified */
        if ( ! http->response.transfer.encoding )
                http->response.transfer.encoding = &http_transfer_identity;

        /* Move to transfer encoding-specific data state */
        transfer = http->response.transfer.encoding;
        http->state = &transfer->state;

        /* Initialise transfer encoding */
        if ( ( rc = transfer->init ( http ) ) != 0 ) {
                DBGC ( http, "HTTP %p could not initialise %s transfer "
                       "encoding: %s\n", http, transfer->name, strerror ( rc ));
                return rc;
        }

        return 0;
}

/** HTTP response headers state */
static struct http_state http_headers = {
        .rx = http_rx_headers,
        .close = http_close_error,
};

/******************************************************************************
 *
 * Identity transfer encoding
 *
 ******************************************************************************
 */

/**
 * Initialise transfer encoding
 *
 * @v http              HTTP transaction
 * @ret rc              Return status code
 */
static int http_init_transfer_identity ( struct http_transaction *http ) {
        int rc;

        /* Complete transfer immediately if we have a zero content length */
        if ( ( http->response.flags & HTTP_RESPONSE_CONTENT_LEN ) &&
             ( http->response.content.len == 0 ) &&
             ( ( rc = http_transfer_complete ( http ) ) != 0 ) )
                return rc;

        return 0;
}

/**
 * Handle received data
 *
 * @v http              HTTP transaction
 * @v iobuf             I/O buffer (may be claimed)
 * @ret rc              Return status code
 */
static int http_rx_transfer_identity ( struct http_transaction *http,
                                       struct io_buffer **iobuf ) {
        size_t len = iob_len ( *iobuf );
        int rc;

        /* Update lengths */
        http->len += len;

        /* Fail if this transfer would overrun the expected content
         * length (if any).
         */
        if ( ( http->response.flags & HTTP_RESPONSE_CONTENT_LEN ) &&
             ( http->len > http->response.content.len ) ) {
                DBGC ( http, "HTTP %p content length overrun\n", http );
                return -EIO_CONTENT_LENGTH;
        }

        /* Hand off to content encoding */
        if ( ( rc = xfer_deliver_iob ( &http->transfer,
                                       iob_disown ( *iobuf ) ) ) != 0 )
                return rc;

        /* Complete transfer if we have received the expected content
         * length (if any).
         */
        if ( ( http->response.flags & HTTP_RESPONSE_CONTENT_LEN ) &&
             ( http->len == http->response.content.len ) &&
             ( ( rc = http_transfer_complete ( http ) ) != 0 ) )
                return rc;

        return 0;
}

/**
 * Handle server connection close
 *
 * @v http              HTTP transaction
 * @v rc                Reason for close
 */
static void http_close_transfer_identity ( struct http_transaction *http,
                                           int rc ) {

        /* Fail if any error occurred */
        if ( rc != 0 )
                goto err;

        /* Fail if we have a content length (since we would have
         * already closed the connection if we had received the
         * correct content length).
         */
        if ( http->response.flags & HTTP_RESPONSE_CONTENT_LEN ) {
                DBGC ( http, "HTTP %p content length underrun\n", http );
                rc = EIO_CONTENT_LENGTH;
                goto err;
        }

        /* Indicate that transfer is complete */
        if ( ( rc = http_transfer_complete ( http ) ) != 0 )
                goto err;

        return;

 err:
        http_close ( http, rc );
}

/** Identity transfer encoding */
static struct http_transfer_encoding http_transfer_identity = {
        .name = "identity",
        .init = http_init_transfer_identity,
        .state = {
                .rx = http_rx_transfer_identity,
                .close = http_close_transfer_identity,
        },
};

/******************************************************************************
 *
 * Chunked transfer encoding
 *
 ******************************************************************************
 */

/**
 * Initialise transfer encoding
 *
 * @v http              HTTP transaction
 * @ret rc              Return status code
 */
static int http_init_transfer_chunked ( struct http_transaction *http ) {

        /* Sanity checks */
        assert ( http->remaining == 0 );
        assert ( http->linebuf.len == 0 );

        return 0;
}

/**
 * Handle received chunk length
 *
 * @v http              HTTP transaction
 * @v iobuf             I/O buffer (may be claimed)
 * @ret rc              Return status code
 */
static int http_rx_chunk_len ( struct http_transaction *http,
                               struct io_buffer **iobuf ) {
        char *line;
        char *endp;
        size_t len;
        int rc;

        /* Receive into temporary line buffer */
        if ( ( rc = http_rx_linebuf ( http, *iobuf, &http->linebuf ) ) != 0 )
                return rc;

        /* Wait until we receive a non-empty line */
        line = buffered_line ( &http->linebuf );
        if ( ( line == NULL ) || ( line[0] == '\0' ) )
                return 0;

        /* Parse chunk length */
        http->remaining = strtoul ( line, &endp, 16 );
        if ( *endp != '\0' ) {
                DBGC ( http, "HTTP %p invalid chunk length \"%s\"\n",
                       http, line );
                return -EINVAL_CHUNK_LENGTH;
        }

        /* Empty line buffer */
        empty_line_buffer ( &http->linebuf );

        /* Update expected length */
        len = ( http->len + http->remaining );
        xfer_seek ( &http->transfer, len );
        xfer_seek ( &http->transfer, http->len );

        /* If chunk length is zero, then move to response trailers state */
        if ( ! http->remaining )
                http->state = &http_trailers;

        return 0;
}

/**
 * Handle received chunk data
 *
 * @v http              HTTP transaction
 * @v iobuf             I/O buffer (may be claimed)
 * @ret rc              Return status code
 */
static int http_rx_chunk_data ( struct http_transaction *http,
                                struct io_buffer **iobuf ) {
        struct io_buffer *payload;
        uint8_t *crlf;
        size_t len;
        int rc;

        /* In the common case of a final chunk in a packet which also
         * includes the terminating CRLF, strip the terminating CRLF
         * (which we would ignore anyway) and hence avoid
         * unnecessarily copying the data.
         */
        if ( iob_len ( *iobuf ) == ( http->remaining + 2 /* CRLF */ ) ) {
                crlf = ( (*iobuf)->data + http->remaining );
                if ( ( crlf[0] == '\r' ) && ( crlf[1] == '\n' ) )
                        iob_unput ( (*iobuf), 2 /* CRLF */ );
        }
        len = iob_len ( *iobuf );

        /* Use whole/partial buffer as applicable */
        if ( len <= http->remaining ) {

                /* Whole buffer is to be consumed: decrease remaining
                 * length and use original I/O buffer as payload.
                 */
                payload = iob_disown ( *iobuf );
                http->len += len;
                http->remaining -= len;

        } else {

                /* Partial buffer is to be consumed: copy data to a
                 * temporary I/O buffer.
                 */
                payload = alloc_iob ( http->remaining );
                if ( ! payload ) {
                        rc = -ENOMEM;
                        goto err;
                }
                memcpy ( iob_put ( payload, http->remaining ), (*iobuf)->data,
                         http->remaining );
                iob_pull ( *iobuf, http->remaining );
                http->len += http->remaining;
                http->remaining = 0;
        }

        /* Hand off to content encoding */
        if ( ( rc = xfer_deliver_iob ( &http->transfer,
                                       iob_disown ( payload ) ) ) != 0 )
                goto err;

        return 0;

 err:
        assert ( payload == NULL );
        return rc;
}

/**
 * Handle received chunked data
 *
 * @v http              HTTP transaction
 * @v iobuf             I/O buffer (may be claimed)
 * @ret rc              Return status code
 */
static int http_rx_transfer_chunked ( struct http_transaction *http,
                                      struct io_buffer **iobuf ) {

        /* Handle as chunk length or chunk data as appropriate */
        if ( http->remaining ) {
                return http_rx_chunk_data ( http, iobuf );
        } else {
                return http_rx_chunk_len ( http, iobuf );
        }
}

/** Chunked transfer encoding */
struct http_transfer_encoding http_transfer_chunked __http_transfer_encoding = {
        .name = "chunked",
        .init = http_init_transfer_chunked,
        .state = {
                .rx = http_rx_transfer_chunked,
                .close = http_close_error,
        },
};

/******************************************************************************
 *
 * Response trailers
 *
 ******************************************************************************
 */

/**
 * Handle received HTTP trailer
 *
 * @v http              HTTP transaction
 * @v iobuf             I/O buffer (may be claimed)
 * @ret rc              Return status code
 */
static int http_rx_trailers ( struct http_transaction *http,
                              struct io_buffer **iobuf ) {
        char *line;
        int rc;

        /* Buffer trailer line */
        if ( ( rc = http_rx_linebuf ( http, *iobuf, &http->linebuf ) ) != 0 )
                return rc;

        /* Wait until we see the empty line marking end of trailers */
        line = buffered_line ( &http->linebuf );
        if ( ( line == NULL ) || ( line[0] != '\0' ) )
                return 0;

        /* Empty line buffer */
        empty_line_buffer ( &http->linebuf );

        /* Transfer is complete */
        if ( ( rc = http_transfer_complete ( http ) ) != 0 )
                return rc;

        return 0;
}

/** HTTP response trailers state */
static struct http_state http_trailers = {
        .rx = http_rx_trailers,
        .close = http_close_error,
};

/******************************************************************************
 *
 * Simple URI openers
 *
 ******************************************************************************
 */

/**
 * Construct HTTP form parameter list
 *
 * @v params            Parameter list
 * @v buf               Buffer to contain HTTP POST parameters
 * @v len               Length of buffer
 * @ret len             Length of parameter list (excluding terminating NUL)
 */
static size_t http_form_params ( struct parameters *params, char *buf,
                                 size_t len ) {
        struct parameter *param;
        ssize_t remaining = len;
        size_t frag_len;

        /* Add each parameter in the form "key=value", joined with "&" */
        len = 0;
        for_each_param ( param, params ) {

                /* Skip non-form parameters */
                if ( ! ( param->flags & PARAMETER_FORM ) )
                        continue;

                /* Add the "&", if applicable */
                if ( len ) {
                        if ( remaining > 0 )
                                *buf = '&';
                        buf++;
                        len++;
                        remaining--;
                }

                /* URI-encode the key */
                frag_len = uri_encode_string ( 0, param->key, buf, remaining );
                buf += frag_len;
                len += frag_len;
                remaining -= frag_len;

                /* Add the "=" */
                if ( remaining > 0 )
                        *buf = '=';
                buf++;
                len++;
                remaining--;

                /* URI-encode the value */
                frag_len = uri_encode_string ( 0, param->value, buf, remaining);
                buf += frag_len;
                len += frag_len;
                remaining -= frag_len;
        }

        /* Ensure string is NUL-terminated even if no parameters are present */
        if ( remaining > 0 )
                *buf = '\0';

        return len;
}

/**
 * Open HTTP transaction for simple URI
 *
 * @v xfer              Data transfer interface
 * @v uri               Request URI
 * @ret rc              Return status code
 */
int http_open_uri ( struct interface *xfer, struct uri *uri ) {
        struct parameters *params = uri->params;
        struct http_request_content content;
        struct http_method *method;
        const char *type;
        void *data;
        size_t len;
        size_t check_len;
        int rc;

        /* Calculate length of form parameter list, if any */
        len = ( params ? http_form_params ( params, NULL, 0 ) : 0 );

        /* Use POST if and only if there are form parameters */
        if ( len ) {

                /* Use POST */
                method = &http_post;
                type = "application/x-www-form-urlencoded";

                /* Allocate temporary form parameter list */
                data = zalloc ( len + 1 /* NUL */ );
                if ( ! data ) {
                        rc = -ENOMEM;
                        goto err_alloc;
                }

                /* Construct temporary form parameter list */
                check_len = http_form_params ( params, data,
                                               ( len + 1 /* NUL */ ) );
                assert ( check_len == len );

        } else {

                /* Use GET */
                method = &http_get;
                type = NULL;
                data = NULL;
        }

        /* Construct request content */
        content.type = type;
        content.data = data;
        content.len = len;

        /* Open HTTP transaction */
        if ( ( rc = http_open ( xfer, method, uri, NULL, &content ) ) != 0 )
                goto err_open;

 err_open:
        free ( data );
 err_alloc:
        return rc;
}

/* Drag in HTTP extensions */
REQUIRING_SYMBOL ( http_open );
REQUIRE_OBJECT ( config_http );