Re: [PATCH v4 1/3] Provide another level of abstraction for the SHA1 utilities.
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Nov 5, 2015, 18:29 UTC
- Message-ID
- <xmqq1tc47117.fsf@gitster.mtv.corp.google.com>
- In-Reply-To
- <1446705523-30701-1-git-send-email-apahlevan@ieee.org>
atousa.p@gmail.com writes:
Show 44 quoted lines
> From: Atousa Pahlevan Duprat <apahlevan@ieee.org> > > The git source uses git_SHA1_Update() and friends to call > into the code that computes the hashes. This is can then be > mapped directly to an implementation that computes the hash, > such as platform_SHA1_Update(); or as we will do in a subsequent > patch, it can be mapped to something more complex that will in turn call > into the platform's SHA implementation. > > Signed-off-by: Atousa Pahlevan Duprat <apahlevan@ieee.org> > --- > cache.h | 19 +++++++++++++++---- > 1 file changed, 15 insertions(+), 4 deletions(-) > > diff --git a/cache.h b/cache.h > index a9aaa03..a934a2e 100644 > --- a/cache.h > +++ b/cache.h > @@ -12,10 +12,21 @@ > > #include SHA1_HEADER > #ifndef git_SHA_CTX > -#define git_SHA_CTX SHA_CTX > -#define git_SHA1_Init SHA1_Init > -#define git_SHA1_Update SHA1_Update > -#define git_SHA1_Final SHA1_Final > + > +/* platform's underlying implementation of SHA1, could be OpenSSL, > + blk_SHA, Apple CommonCrypto, etc... */ > +#define platform_SHA_CTX SHA_CTX > +#define platform_SHA1_Init SHA1_Init > +#define platform_SHA1_Update SHA1_Update > +#define platform_SHA1_Final SHA1_Final > + > +/* git may call platform's underlying implementation of SHA1 directly, > + or may call it through a wrapper */ > +#define git_SHA_CTX platform_SHA_CTX > +#define git_SHA1_Init platform_SHA1_Init > +#define git_SHA1_Update platform_SHA1_Update > +#define git_SHA1_Final platform_SHA1_Final > + > #endif > > #include <zlib.h>
This is not quite correct, I am afraid. Our own implementations still define git_SHA* macros, but they should be considered the "platform" ones in the new world order with another level of indirection.
I think the attached is closer to what we want. The implementations may give us platform_SHA*() in which case cache.h does not have to give the fallback mapping from them to the OpenSSL compatible interface used by OpenSSL and CommonCrypto. Regardless of the platform SHA-1 implementations, by default they are the ones used by the rest of the system via git_SHA*().
And in the second step, git_SHA1_Update() may map to the Chunked one, whose implementation would use platform_SHA1_Update().
-- >8 --- From: Atousa Pahlevan Duprat <apahlevan@ieee.org> Subject: sha1: provide another level of indirection for the SHA-1 functions
The git source uses git_SHA1_Update() and friends to call into the code that computes the hashes. Traditionally, we used to map these directly to underlying implementation of the SHA-1 hash (e.g. SHA1_Update() from OpenSSL or blk_SHA1_Update() from block-sha1/).
This arrangement however makes it hard to tweak behaviour of the underlying implementation without fully replacing. If we want to introduce a tweaked_SHA1_Update() wrapper to implement the "Update" in a slightly different way, for example, the implementation of the wrapper still would want to call into the underlying implementation, but tweaked_SHA1_Update() cannot call git_SHA1_Update() to get to the underlying implementation (often but not always SHA1_Update()).
Add another level of indirection that maps platform_SHA1_Update() and friends to their underlying implementations, and by default make git_SHA1_Update() and friends map to platform_SHA1_* functions.
Doing it this way will later allow us to map git_SHA1_Update() to tweaked_SHA1_Update(), and the latter can use platform_SHA1_Update() in its implementation.
Signed-off-by: Atousa Pahlevan Duprat <apahlevan@ieee.org> Signed-off-by: Junio C Hamano <gitster@pobox.com> --- block-sha1/sha1.h | 8 ++++---- cache.h | 22 +++++++++++++++++----- ppc/sha1.h | 8 ++++---- 3 files changed, 25 insertions(+), 13 deletions(-)
diff --git a/block-sha1/sha1.h b/block-sha1/sha1.h index b864df6..4df6747 100644 --- a/block-sha1/sha1.h +++ b/block-sha1/sha1.h @@ -16,7 +16,7 @@ void blk_SHA1_Init(blk_SHA_CTX *ctx); void blk_SHA1_Update(blk_SHA_CTX *ctx, const void *dataIn, unsigned long len); void blk_SHA1_Final(unsigned char hashout[20], blk_SHA_CTX *ctx); -#define git_SHA_CTX blk_SHA_CTX -#define git_SHA1_Init blk_SHA1_Init -#define git_SHA1_Update blk_SHA1_Update -#define git_SHA1_Final blk_SHA1_Final +#define platform_SHA_CTX blk_SHA_CTX +#define platform_SHA1_Init blk_SHA1_Init +#define platform_SHA1_Update blk_SHA1_Update +#define platform_SHA1_Final blk_SHA1_Final diff --git a/cache.h b/cache.h index a9aaa03..2f697c4 100644 --- a/cache.h +++ b/cache.h @@ -11,13 +11,25 @@ #include "string-list.h" #include SHA1_HEADER -#ifndef git_SHA_CTX -#define git_SHA_CTX SHA_CTX -#define git_SHA1_Init SHA1_Init -#define git_SHA1_Update SHA1_Update -#define git_SHA1_Final SHA1_Final +#ifndef platform_SHA_CTX +/* + * platform's underlying implementation of SHA-1; could be OpenSSL, + * blk_SHA, Apple CommonCrypto, etc... Note that including + * SHA1_HEADER may have already defined platform_SHA_CTX for our + * own implementations like block-sha1 and ppc-sha1, so we list + * the default for OpenSSL compatible SHA-1 implementations here. + */ +#define platform_SHA_CTX SHA_CTX +#define platform_SHA1_Init SHA1_Init +#define platform_SHA1_Update SHA1_Update +#define platform_SHA1_Final SHA1_Final #endif +#define git_SHA_CTX platform_SHA_CTX +#define git_SHA1_Init platform_SHA1_Init +#define git_SHA1_Update platform_SHA1_Update +#define git_SHA1_Final platform_SHA1_Final + #include <zlib.h> typedef struct git_zstream { z_stream z; diff --git a/ppc/sha1.h b/ppc/sha1.h index c405f73..9b24b32 100644 --- a/ppc/sha1.h +++ b/ppc/sha1.h @@ -19,7 +19,7 @@ int ppc_SHA1_Init(ppc_SHA_CTX *c); int ppc_SHA1_Update(ppc_SHA_CTX *c, const void *p, unsigned long n); int ppc_SHA1_Final(unsigned char *hash, ppc_SHA_CTX *c); -#define git_SHA_CTX ppc_SHA_CTX -#define git_SHA1_Init ppc_SHA1_Init -#define git_SHA1_Update ppc_SHA1_Update -#define git_SHA1_Final ppc_SHA1_Final +#define platform_SHA_CTX ppc_SHA_CTX +#define platform_SHA1_Init ppc_SHA1_Init +#define platform_SHA1_Update ppc_SHA1_Update +#define platform_SHA1_Final ppc_SHA1_Final
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