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.TH scan_asn1derlength 3
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.SH NAME
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scan_asn1derlengthvalue \- decode an unsigned integer from ASN.1 DER length encoding
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.SH SYNTAX
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.B #include <libowfat/scan.h>
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size_t \fBscan_asn1derlengthvalue\fP(const char *\fIsrc\fR,size_t \fIlen\fR,unsigned long long *\fIdest\fR);
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.SH DESCRIPTION
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scan_asn1derlengthvalue decodes an unsigned integer in ASN.1 DER length encoding
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from a memory area holding binary data. It writes the decode value in
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\fIdest\fR and returns the number of bytes it read from \fIsrc\fR.
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scan_asn1derlength never reads more than \fIlen\fR bytes from \fIsrc\fR. If the
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sequence is longer than that, or the memory area contains an invalid
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sequence, scan_asn1derlength returns 0 and does not touch \fIdest\fR.
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The length of the longest spec-compliant ASN.1 DER length is 128 bytes,
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but this implementation will return an error if the value does not fit
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into the target integer type. In practice the largest sequence is
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sizeof(*dest)+1.
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This implementation will reject values that are not encoded in the
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minimum amount of bytes.
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If you need to decode the length value so you can parse actual ASN.1
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tag/length/value structures, please consider using scan_asn1derlength
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instead, as it will do additional checking for you.
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.SH "SEE ALSO"
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fmt_asn1derlength(3), scan_asn1derlengthvalue(3)
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