# dkim_get_sigsubstring()

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SYNOPSIS |
    #include <dkim.h>
    DKIM_STAT dkim_get_sigsubstring(
    	DKIM *dkim,
    	DKIM_SIGINFO *sig,
            char *buf,
            size_t *buflen
    );
Retrieve a minimal substring of the actual signature (i.e. the "b=" tag value) from a specified signature, of sufficient length to identify this signature uniquely from others.
DESCRIPTION |
Called When | `dkim_getsig()` is called after `dkim_eom()` when `dkim` is a verifying handle, i.e. one returned by an earlier call to `dkim_verify()`.
ARGUMENTS |
Argument | Description
--- | ---
dkim | Message-specific handle, returned by `dkim_sign()`.
sig | Signature-specific handle, retrieved by a prior call to `dkim_getsiglist()`.
buf | Pointer to a buffer that should receive a minimal unique substring of the digital signature portion of `sig`.
buflen | The address of an integer that should contain the number of bytes available at `buf` and will be updated to contain the number of bytes needed to produce a minimal substring.
NOTES | No fewer than eight bytes will be requested. If two or more signatures have the same initial byte sequences in "b=" tags, larger lengths will be required, theoretically requiring as much as the entire signature. If the size of `buf` is too small to contain the minimal substring of `sig`, `DKIM_STAT_NORESOURCE` is returned, `buflen` will be updated to indicate the minimal number of bytes required, and `buf` will be unchanged. The string written to `buf` will be NULL-terminated unless the provided buffer is exactly the right size to contain the output.

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