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mateuszvis |
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/*
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* unpacks a http "chunked" transfer into a raw data stream.
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* this file is part of the pkgnet tool from the SvarDOS project.
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*
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* Copyright (C) 2021 Mateusz Viste
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*/
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#include <stdlib.h> /* atol() */
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#include <string.h>
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#include "unchunk.h"
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/* transforms a http CHUNKED stream into actual data, returns the amount of raw data to read */
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int unchunk(unsigned char *buff, int bufflen) {
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static long bytesleft; /* how many bytes are expected yet in the ongoing chunk */
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static char partial_hdr[16]; /* a small buffer for storing partial chunk headers, if these are transmitted in separate parts */
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int hdrstart, hdrend;
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/* if chunk header was being in progress, try to decode it now */
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if (bytesleft == -1) {
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int partial_hdr_len = strlen(partial_hdr);
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/* locate header terminator, if available */
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for (hdrend = 0; (hdrend < bufflen) && (buff[hdrend] != '\n'); hdrend++);
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if (partial_hdr_len + hdrend > 15) return(-1); /* error: chunk header too long */
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/* copy header to buffer */
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memcpy(partial_hdr + partial_hdr_len, buff, hdrend);
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partial_hdr[partial_hdr_len + hdrend] = 0;
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/* quit if header still no complete */
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if (hdrend >= bufflen) return(0);
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/* good, got whole header */
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bufflen -= hdrend + 1;
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memmove(buff, buff + hdrend + 1, bufflen);
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bytesleft = strtol(partial_hdr, NULL, 16);
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}
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AGAIN:
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if (bufflen <= bytesleft) { /* bufflen <= bytesleft */
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bytesleft -= bufflen;
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return(bufflen);
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}
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/* else bufflen > bytesleft */
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/* skip trailing \r\n after chunk */
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for (hdrstart = bytesleft; hdrstart < bufflen; hdrstart++) if ((buff[hdrstart] != '\r') && (buff[hdrstart] != '\n')) break;
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/* skip chunk size (look for its \n terminator) */
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for (hdrend = hdrstart; (hdrend < bufflen) && (buff[hdrend] != '\n'); hdrend++);
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if (hdrend < bufflen) { /* full header found */
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long newchunklen;
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/* read the header length */
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newchunklen = strtol((char *)buff + hdrstart, NULL, 16);
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/* move data over header to get a contiguous block of data */
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memmove(buff + bytesleft, buff + hdrend + 1, bufflen - (hdrend + 1));
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bufflen -= (hdrend + 1 - bytesleft);
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/* update bytesleft */
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bytesleft += newchunklen;
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/* loop again */
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goto AGAIN;
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} else { /* partial header */
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if ((bufflen - bytesleft) > 15) return(-1); /* error: chunk header appears to be longer than 15 characters */
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memset(partial_hdr, 0, sizeof(partial_hdr));
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memcpy(partial_hdr, buff + bytesleft, bufflen - bytesleft);
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bufflen -= (bufflen - bytesleft);
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bytesleft = -1; /* "header in progress" */
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return(bufflen);
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}
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}
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