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message-digest

Documentation

Message Digest provides support for message digest primitives. A message-digest is a function taking an arbitrary input and returning a fixed-length hash. For best results the input should be something easily treated as a byte-block.

make-binary-message-digest

[procedure] (make-binary-message-digest SOURCE CONTEXT-INFO DIGEST-LENGTH INIT UPDATE FINAL [CALLER]) => STRING

Returns the message-digest for SOURCE as a string of bytes.

SOURCE is any Scheme-object. See the UPDATE entry below for interpretation of the SOURCE.

CONTEXT-INFO is either a procedure that returns an object CONTEXT, or a positive fixnum. When a fixnum a memory-block of length CONTEXT-INFO is allocated (and automatically free'ed). The CONTEXT is often a pointer but maybe any Scheme-object.

DIGEST-LENGTH is the fixnum count of bytes in the result string.

The phase procedures:

(INIT CONTEXT)

Initialization phase procedure. Sets up the CONTEXT, if necessary. The result is ignored.

(UPDATE CONTEXT BUFFER COUNT)

Accumulation phase procedure. Must accumulate the BUFFER, where BUFFER is a Scheme-object. Will be called one or more times. The result is ignored.

Where SOURCE is-a:

string
BUFFER = SOURCE.
blob
BUFFER = SOURCE.
procedure
updates with BUFFER = (procedure) until #f = (procedure).
input-port
like procedure above but from message-digest-chunk-reader.
object
BUFFER = (message-digest-chunk-converter SOURCE).

Where the actual number of bytes in the BUFFER can be determined COUNT will be a positive-integer. Otherwise COUNT is -1.

See message-digest-chunk-size to set the number of bytes read per update invocation.

See message-digest-chunk-reader to set the chunk reader procedure creator.

See message-digest-chunk-converter to set the chunk representation translation procedure.

(FINAL CONTEXT RESULT)

Finalization phase procedure. Must build the resulting message-digest in the supplied RESULT string of length DIGEST-LENGTH. The result is ignored.

The optional CALLER is for identification.

make-message-digest

[procedure] (make-message-digest SOURCE CONTEXT-INFO DIGEST-LENGTH INIT UPDATE FINAL [CALLER]) => STRING

Exactly as above but returns the message-digest for SOURCE using byte-string->hexadecimal.

message-digest-primitive

[procedure] (make-message-digest-primitive CONTEXT-INFO DIGEST-LENGTH INIT UPDATE FINAL ID)

Create a message-digest-primitive record object. The meaning of the fields are exactly as above. Predicates and accessors follow:

[procedure] (message-digest-primitive? OBJ)
[procedure] (message-digest-primitive-context-info PRIMITIVE)
[procedure] (message-digest-primitive-digest-length PRIMITIVE)
[procedure] (message-digest-primitive-init PRIMITIVE)
[procedure] (message-digest-primitive-update PRIMITIVE)
[procedure] (message-digest-primitive-final PRIMITIVE)
[procedure] (message-digest-primitive-name PRIMITIVE)

message-digest-primitive-apply

[procedure] (message-digest-primitive-apply MESSAGE-DIGEST-PRIMITIVE SOURCE [CALLER])

Returns a binary-message-digest of SOURCE using MESSAGE-DIGEST-PRIMITIVE.

Parameters

message-digest-chunk-size

[parameter] (message-digest-chunk-size [SIZE])

The number of bytes to read during the message-digest update phase. SIZE is a positive fixnum, default 1024.

message-digest-chunk-reader

[parameter] (message-digest-chunk-reader [READER-CREATOR])

The procedure used to create an input procedure.

[procedure] (READER-CREATOR INPUT-PORT) => PROCEDURE/0

The default READER-CREATOR will return a reader that takes from INPUT-PORT in (message-digest-chunk-size) bytes. The INPUT-PORT is treated as a binary-stream no matter how it is defined.

message-digest-chunk-converter

[parameter] (message-digest-chunk-converter [CONVERTER])

The procedure used to translate an arbitrary Scheme-object into something suitable for an UPDATE procedure. Should the CONVERTER be #f then no translation is attempted.

[procedure] (CONVERTER OBJECT) => OBJECT

The default CONVERTER will convert a heterogeneous-vector to a blob with shared-storage. No translation otherwise.

Auxillary Procedures

byte-string->substring-list

[procedure] (byte-string->substring-list STRING CHUNK-SIZE [START [END]]) => LIST

Returns a list of CHUNK-SIZE substrings of STRING, on the interval [START END). Defaults are [0 string-length).

Any remaining substring less than CHUNK-SIZE is appended to the list.

byte-string->substring-list/shared

[procedure] (byte-string->substring-list/shared STRING CHUNK-SIZE [START [END]]) => LIST

Returns a list of CHUNK-SIZE substrings of STRING, on the interval [START END). Defaults are [0 byte-string-length).

Any remaining substring less than CHUNK-SIZE is appended to the list.

The substrings can share storage with the STRING!

byte-string->hexadecimal

[procedure] (byte-string->hexadecimal STRING [START [END]]) => STRING

Returns a hex-encoded representation of STRING, on the interval [START END). Defaults are [0 byte-string-length).

Examples

Here's an example for creating a digest from the output of a procedure that expects to be called with an output port argument:

(use message-digest)

(define (call-with-output-digest primitive proc)
  (let* ((ctx-info (message-digest-primitive-context-info primitive))
         (update-digest (message-digest-primitive-update primitive))
         ;; Create new context, by allocating manually or calling the procedure
         (ctx (if (procedure? ctx-info) (ctx-info) (allocate ctx-info)))
	 ;; Create a procedure that updates the digest based on a string
         (update (lambda (str) (update-digest ctx str (string-length str))))
	 ;; Make a port that invokes the updater when written to
         (outport (make-output-port update void)))
    (handle-exceptions exn
      ;; If something goes wrong, clean up the context if we allocated it
      (begin (unless (procedure? ctx-info) (free ctx)) (signal exn))
      (let ((result (make-string
                     (message-digest-primitive-digest-length primitive))))
        ((message-digest-primitive-init primitive) ctx)
        (proc outport)
        ((message-digest-primitive-final primitive) ctx result)
	;; Don't forget to free the context if we allocated it
        (unless (procedure? ctx-info) (free ctx))
	;; Output is a byte string.  Convert to a hex number:
        (byte-string->hexadecimal result)))))

;; Usage:
(use md5)    ; Or sha1, or sha2, ...

(call-with-output-digest
  (md5-primitive)
  (lambda (out)
    (display "foo" out)))

Notes

Requirements

miscmacros check-errors

Bugs and Limitations

Author

kon lovett

Version history
2.0.1
Bug fix for (message-digest-chunk-converter) use by make-binary-message-digest.
2.0.0
Release for Chicken 4 [From a diff provided by Christian Kellermann]

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