forked from osmocom/wireshark
If you're doing TCP reassembly by hand rather than with
tcp_dissect_pdus(), pinfo->desegment_len indicates whether your dissector needs more data from TCP or not - the return value doesn't indicate that. Fix typo. It appears that the Id keyword is one of the case-insensitive ones in the svn:keywords property, so if you set it to "ID" it still expands "$Id$"; it also appears not to expand "$ID$". We use Revision, Date, and Author in the document to indicate the revision, and don't expand Id, so that references to "$Id$" get left alone. Rewrap paragraphs. svn path=/trunk/; revision=19950
This commit is contained in:
Guy Harris
parent
45aa24f1ec
commit
9bf2e75f68
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@ -1,4 +1,6 @@
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$ID$
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$Revision$
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$Date$
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$Author$
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This file is a HOWTO for Wireshark developers. It describes how to start coding
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a Wireshark protocol dissector and the use some of the important functions and
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@ -25,7 +27,7 @@ You'll find additional information in the following README files:
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- README.capture - the capture engine internals
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- README.design - Wireshark software design - incomplete
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- READEM.developer - this file
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- README.developer - this file
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- README.display_filter - Display Filter Engine
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- README.idl2wrs - CORBA IDL converter
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- README.packaging - how to distribute a software package containing WS
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@ -3136,16 +3138,15 @@ The arguments to tcp_dissect_pdus are:
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The second reassembly mode is preferred when the dissector cannot determine
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how many bytes it will need to read in order to determine the size of a PDU.
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For this mode it is recommended that your dissector be the newer dissector
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type which returns "int" rather than the older type which returned "void".
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This reassembly mode relies on Wireshark's mechanism for processing multiple PDUs
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per frame. When a dissector processes a PDU from a tvbuff the PDU may not be
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aligned to a frame of the underlying protocol. Wireshark allows dissectors to
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process PDUs in an idempotent way--dissectors only need to consider one PDU at a
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time. If your dissector discovers that it can not process a complete PDU from
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the current tvbuff the dissector should halt processing and request additional
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bytes from the lower level dissector.
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This reassembly mode relies on Wireshark's mechanism for processing
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multiple PDUs per frame. When a dissector processes a PDU from a tvbuff
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the PDU may not be aligned to a frame of the underlying protocol.
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Wireshark allows dissectors to process PDUs in an idempotent
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way--dissectors only need to consider one PDU at a time. If your
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dissector discovers that it can not process a complete PDU from the
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current tvbuff the dissector should halt processing and request
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additional bytes from the lower level dissector.
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Your dissect_PROTO will be called by the lower level dissector whenever
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sufficient new bytes become available. Each time your dissector is called it is
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@ -3155,20 +3156,19 @@ should examine the tvbuff provided and determine if an entire PDU is available.
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If sufficient bytes are available the dissector processes the PDU and returns
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the length of the PDU from your dissect_PROTO.
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Completion of a PDU is signified by dissect_PROTO returning a positive value.
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The value is the number of bytes which were processed from the tvbuff. If there
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were insufficient bytes in the tvbuff to complete a PDU then the dissect_PROTO
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returns a negative value requesting additional bytes. The negative return value
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indicates how many additional bytes are required. Additionally dissect_PROTO
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must update the pinfo structure to indicate that more bytes are required. The
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desegment_offset field is the offset in the tvbuff at which the dissector will
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continue processing when next called. The desegment_len field should contain the
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estimated number of additional bytes required for completing the PDU. The
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dissect_PROTO will not be called again until the specified number of bytes are
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available. pinfo->desegment_len may be set to -1 if dissect_PROTO cannot
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determine how many additional bytes are required. Dissectors should set the
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desegment_len to a reasonable value when possible rather than always setting
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-1 as it will generally be more efficient.
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Completion of a PDU is signified by dissect_PROTO returning a positive
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value. The value is the number of bytes which were processed from the
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tvbuff. If there were insufficient bytes in the tvbuff to complete a
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PDU then dissect_PROTO must update the pinfo structure to indicate that
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more bytes are required. The desegment_offset field is the offset in
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the tvbuff at which the dissector will continue processing when next
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called. The desegment_len field should contain the estimated number of
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additional bytes required for completing the PDU. The dissect_PROTO
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will not be called again until the specified number of bytes are
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available. pinfo->desegment_len may be set to -1 if dissect_PROTO
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cannot determine how many additional bytes are required. Dissectors
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should set the desegment_len to a reasonable value when possible rather
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than always setting -1 as it will generally be more efficient.
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static hf_register_info hf[] = {
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{&hf_cstring,
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@ -3183,10 +3183,8 @@ static hf_register_info hf[] = {
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* @param tvb The buffer to dissect.
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* @param pinfo Packet Info.
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* @param tree The protocol tree.
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* @return Number of bytes from the tvbuff_t which were processed or a negative
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* value indicating more bytes are needed.
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**/
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static int dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)
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static void dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)
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{
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guint offset = 0;
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gint available = tvb_reported_length_remaining(tvb, offset);
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@ -3196,7 +3194,7 @@ static int dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)
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/* No '\0' found, ask for another byte. */
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pinfo->desegment_offset = offset;
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pinfo->desegment_len = 1;
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return -1;
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return;
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}
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if (check_col(pinfo->cinfo, COL_INFO)) {
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@ -3208,8 +3206,6 @@ static int dissect_cstr(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree)
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if (tree) {
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proto_tree_add_item(tree, hf_cstring, tvb, offset, len, FALSE);
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}
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return len;
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}
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This simple dissector will repeatedly return -1 requesting one more byte until
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@ -3287,4 +3283,3 @@ ptvcursor_tree(ptvcursor_t*)
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void
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ptvcursor_set_tree(ptvcursor_t*, proto_tree *)
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sets a new proto_tree for the ptvcursor
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