pack.c: add an offset argument to unpack and unpack1

[Feature #18254]

This is useful to avoid repeteadly copying strings when parsing binary formats

1 files changed, 20 insertions, 0 deletions

diff --git a/spec/ruby/core/string/unpack1_spec.rb b/spec/ruby/core/string/unpack1_spec.rb
index 5fe81733fb..f59bd92d6a 100644
--- a/spec/ruby/core/string/unpack1_spec.rb
+++ b/spec/ruby/core/string/unpack1_spec.rb
@@ -7,4 +7,24 @@ describe "String#unpack1" do
     "aG9nZWZ1Z2E=".unpack1("m").should == "hogefuga"
     "A".unpack1("B*").should == "01000001"
   end
+
+  ruby_version_is "3.1" do
+    it "starts unpacking from the given offset" do
+      "ZZABCD".unpack1('x3C', offset: 2).should == "ABCD".unpack('x3C')[0]
+      "ZZZZaG9nZWZ1Z2E=".unpack1("m", offset: 4).should == "hogefuga"
+      "ZA".unpack1("B*", offset: 1).should == "01000001"
+    end
+
+    it "raises an ArgumentError when the offset is negative" do
+      -> { "a".unpack1("C", offset: -1) }.should raise_error(ArgumentError)
+    end
+
+    it "returns nil if the offset is at the end of the string" do
+      "a".unpack1("C", offset: 1).should == nil
+    end
+
+    it "raises an ArgumentError when the offset is larget than the string" do
+      -> { "a".unpack1("C", offset: 2) }.should raise_error(ArgumentError)
+    end
+  end
 end