Add HexSHA256File for computing the SHA256 checksum of a file

doc/ref/string.xml

@@ -691,6 +691,7 @@ gap> HexStringInt(last);
 <#Include Label="EvalString">
 <#Include Label="CrcString">
 <#Include Label="HexSHA256">
+<#Include Label="HexSHA256File">
 <#Include Label="Pluralize">
 
 </Section>

lib/files.gd

@@ -850,5 +850,44 @@ DeclareGlobalFunction( "Edit" );
 ##
 DeclareGlobalFunction("HexSHA256");
 
+
+##  <#GAPDoc Label="HexSHA256File">
+##  <ManSection>
+##  <Func Name="HexSHA256File" Arg='filename, decompress'/>
+##
+##  <Description>
+##  <Index>hash function</Index>
+##  <Index>checksum</Index>
+##  Return the SHA-256 cryptographic checksum of the contents of the file
+##  <A>filename</A>, as a string with 64 lowercase hexadecimal digits,
+##  or <K>fail</K> if the file cannot be read.
+##  <P/>
+##  The file is read as binary data, so the result always describes the bytes
+##  on disk, also on systems which distinguish text and binary mode and would
+##  otherwise translate line endings.  It is read in chunks, so the size of
+##  the file is not limited by the available memory.
+##  <P/>
+##  <A>decompress</A> must be <K>true</K> or <K>false</K>, and says which of
+##  two different checksums is wanted: with <K>true</K>, a file whose name
+##  ends in <C>.gz</C> is decompressed while reading, so that the checksum
+##  describes the data as <Ref Func="StringFile" BookName="gapdoc"/> would
+##  read it; with <K>false</K>, it describes the bytes on disk, which is what
+##  one wants in order to compare against a checksum published alongside a
+##  file.  There is no default, because everything else in &GAP; decompresses
+##  and silently doing the opposite would be a trap.
+##  <Log><![CDATA[
+##  gap> name := Filename(DirectoryTemporary(), "test.txt");;
+##  gap> FileString(name, "abcd");;
+##  gap> HexSHA256File(name, false);
+##  "88d4266fd4e6338d13b845fcf289579d209c897823b9217da3e161936f031589"
+##  gap> HexSHA256File("/no/such/file", false);
+##  fail
+##  ]]></Log>
+##  </Description>
+##  </ManSection>
+##  <#/GAPDoc>
+##
+DeclareGlobalFunction("HexSHA256File");
+
 BIND_GLOBAL("GAP_SHA256_State_Type",
            NewType(NewFamily("GAP_SHA256_State_Family"), IsObject) );

lib/files.gi

@@ -393,30 +393,55 @@ InstallGlobalFunction(RemoveDirectoryRecursively,
     return Dowork(dirname);
   end );
 
+BindGlobal( "GAP_SHA256_HexOfWords",
+function(words)
+    local res;
+
+    res := Sum([0..7], i -> words[8-i]*2^(32*i));
+    res := LowercaseString(HexStringInt(res));
+    # HexStringInt drops leading zero digits, but a SHA256 digest is always
+    # 256 bits = 64 hex digits, so left-pad with '0' if the top byte(s) were 0.
+    if Length(res) < 64 then
+        res := Concatenation(ListWithIdenticalEntries(64 - Length(res), '0'), res);
+    fi;
+    return res;
+end);
+
 InstallGlobalFunction( HexSHA256,
 function(str)
-    local s, res;
+    local s, chunk;
 
+    s := GAP_SHA256_INIT();
     if IsString(str) then
-        str := CopyToStringRep(str);
+        GAP_SHA256_UPDATE(s, CopyToStringRep(str));
     elif IsInputStream(str) then
-        str := ReadAll(str);
-        # TODO: instead o reading the complete stream at once (which might be
-        # huge), it would be better to read it in chunks, say 16kb at a time.
-        # Alas, our streams API currently offers no way to do that.
+        # read in chunks: the stream may deliver more than fits in memory
+        repeat
+            chunk := ReadAll(str, 65536);
+            if IsString(chunk) and Length(chunk) > 0 then
+                GAP_SHA256_UPDATE(s, CopyToStringRep(chunk));
+            fi;
+        until not IsString(chunk) or Length(chunk) = 0;
     else
         ErrorNoReturn("<str> has to be a string or an input stream");
     fi;
 
-    s := GAP_SHA256_INIT();
-    GAP_SHA256_UPDATE(s, str);
-    res := GAP_SHA256_FINAL(s);
-    res := Sum([0..7], i -> res[8-i]*2^(32*i));;
-    res := LowercaseString(HexStringInt(res));
-    # HexStringInt drops leading zero digits, but a SHA256 digest is always
-    # 256 bits = 64 hex digits, so left-pad with '0' if the top byte(s) were 0.
-    if Length(res) < 64 then
-        res := Concatenation(ListWithIdenticalEntries(64 - Length(res), '0'), res);
+    return GAP_SHA256_HexOfWords(GAP_SHA256_FINAL(s));
+end);
+
+InstallGlobalFunction( HexSHA256File,
+function(filename, decompress)
+    local res;
+
+    if not IsString(filename) then
+        ErrorNoReturn("<filename> must be a string");
+    elif not decompress in [ true, false ] then
+        ErrorNoReturn("<decompress> must be 'true' or 'false'");
     fi;
-    return res;
+
+    res := GAP_SHA256_FILE(UserHomeExpand(filename), decompress);
+    if res = fail then
+        return fail;
+    fi;
+    return GAP_SHA256_HexOfWords(res);
 end);

src/sha256.c

@@ -17,6 +17,7 @@
 #include "objects.h"
 #include "plist.h"
 #include "stringobj.h"
+#include "sysfiles.h"
 
 #include "config.h"
 
@@ -295,6 +296,44 @@ Obj FuncGAP_SHA256_FINAL(Obj self, Obj state)
     return result;
 }
 
+Obj FuncGAP_SHA256_FILE(Obj self, Obj filename, Obj decompress)
+{
+    Obj            result;
+    sha256_state_t st;
+    Int            fid, len;
+    int            i;
+    UChar          buf[16384];
+
+    RequireStringRep(SELF_NAME, filename);
+    RequireTrueOrFalse(SELF_NAME, decompress);
+
+    // Mode "rb" rather than "r" so that no line ending translation happens;
+    // the digest has to describe the bytes on disk.  With <decompress> set,
+    // a file whose name ends in '.gz' is hashed as its decompressed content
+    // instead, matching what 'InputTextFile' would read.
+    fid = SyFopen(CONST_CSTR_STRING(filename), "rb", decompress == True);
+    if (fid == -1)
+        return Fail;
+
+    sha256_init(&st);
+    while ((len = SyRead(fid, buf, sizeof(buf))) > 0) {
+        sha256_update(&st, buf, len);
+    }
+    SyFclose(fid);
+    if (len < 0)
+        return Fail;
+
+    sha256_final(&st);
+
+    result = NEW_PLIST(T_PLIST, 8);
+    SET_LEN_PLIST(result, 8);
+    for (i = 0; i < 8; i++) {
+        SET_ELM_PLIST(result, i + 1, ObjInt_UInt(st.r[i]));
+        CHANGED_BAG(result);
+    }
+    return result;
+}
+
 Obj FuncGAP_SHA256_HMAC(Obj self, Obj key, Obj text)
 {
     UInt           i, klen;
@@ -355,6 +394,7 @@ static StructGVarFunc GVarFuncs[] = {
     GVAR_FUNC_0ARGS(GAP_SHA256_INIT),
     GVAR_FUNC_2ARGS(GAP_SHA256_UPDATE, state, bytes),
     GVAR_FUNC_1ARGS(GAP_SHA256_FINAL, state),
+    GVAR_FUNC_2ARGS(GAP_SHA256_FILE, filename, decompress),
     GVAR_FUNC_2ARGS(GAP_SHA256_HMAC, key, text),
 
     { 0 }    // Finish with an empty entry

tst/testinstall/sha256.tst

@@ -1,4 +1,5 @@
 #
+#@local dir, gzname, name, out, state, str
 gap> START_TEST("sha256.tst");
 
 #
@@ -57,5 +58,43 @@ gap> HexSHA256(InputTextString("abcd\r\n"));
 gap> HexSHA256(InputTextString(""));
 "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
 
+# HexSHA256File
+gap> dir := DirectoryTemporary();;
+gap> name := Filename(dir, "test.txt");;
+gap> FileString(name, "abcd");;
+gap> HexSHA256File(name, false);
+"88d4266fd4e6338d13b845fcf289579d209c897823b9217da3e161936f031589"
+gap> FileString(Filename(dir, "empty.txt"), "");;
+gap> HexSHA256File(Filename(dir, "empty.txt"), false);
+"e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+
+# larger than the read buffer, so that more than one chunk gets hashed
+gap> str := Concatenation(List([1 .. 5000], i -> "0123456789"));;
+gap> FileString(Filename(dir, "big.txt"), str);;
+gap> HexSHA256File(Filename(dir, "big.txt"), false) = HexSHA256(str);
+true
+
+# a file that is not there
+gap> HexSHA256File(Filename(dir, "no-such-file"), false);
+fail
+
+# the two answers a '.gz' file has
+gap> gzname := Filename(dir, "compressed.txt.gz");;
+gap> out := OutputGzipFile(gzname, false);;
+gap> WriteAll(out, "abcd");;
+gap> CloseStream(out);
+gap> HexSHA256File(gzname, false) = HexSHA256("abcd");
+false
+gap> HexSHA256File(gzname, true) = HexSHA256("abcd");
+true
+
+# argument checking
+gap> HexSHA256File(name);
+Error, Function: number of arguments must be 2 (not 1)
+gap> HexSHA256File(42, false);
+Error, <filename> must be a string
+gap> HexSHA256File(name, "yes");
+Error, <decompress> must be 'true' or 'false'
+
 #
 gap> STOP_TEST("sha256.tst");