2 files changed, 64 insertions, 25 deletions

diff --git a/dedup/debpkg.py b/dedup/debpkg.py
index 8f2121b..04773de 100644
--- a/dedup/debpkg.py
+++ b/dedup/debpkg.py
@@ -1,5 +1,6 @@
 from debian import deb822
 
+from dedup.arreader import ArReader
 from dedup.hashing import hash_file
 
 def process_control(control_contents):
@@ -53,3 +54,33 @@ def get_tar_hashes(tar, hash_functions):
             if hashvalue:
                 hashes[hashobj.name] = hashvalue
         yield (elem.name, elem.size, hashes)
+
+class DebExtractor(object):
+    "Base class for extracting desired features from a Debian package."
+
+    def process(self, filelike):
+        """Process a Debian package.
+        @param filelike: is a file-like object containing the contents of the
+                         Debian packge and can be read once without seeks.
+        """
+        af = ArReader(filelike)
+        af.read_magic()
+        while True:
+            try:
+                name = af.read_entry()
+            except EOFError:
+                break
+            else:
+                self.handle_ar_member(name, af)
+        self.handle_ar_end()
+
+    def handle_ar_member(self, name, filelike):
+        """Handle an ar archive member of the Debian package.
+        @type name: bytes
+        @param name: is the name of the member
+        @param filelike: is a file-like object containing the contents of the
+                         member and can be read once without seeks.
+        """
+
+    def handle_ar_end(self):
+        "Handle the end of the ar archive of the Debian package."
diff --git a/importpkg.py b/importpkg.py
index f72cf03..0798f13 100755
--- a/importpkg.py
+++ b/importpkg.py
@@ -14,8 +14,7 @@ import zlib
 import lzma
 import yaml
 
-from dedup.arreader import ArReader
-from dedup.debpkg import process_control, get_tar_hashes
+from dedup.debpkg import DebExtractor, process_control, get_tar_hashes
 from dedup.hashing import DecompressedHash, SuppressingHash, HashedStream, \
         HashBlacklistContent
 from dedup.compression import GzipDecompressor, DecompressedStream
@@ -54,42 +53,46 @@ def decompress_tar(filelike, extension):
     return tarfile.open(fileobj=filelike,
                         mode="r|" + extension[1:].decode("ascii"))
 
-def process_package(filelike, hash_functions, callback):
-    af = ArReader(filelike)
-    af.read_magic()
-    state = "start"
-    while True:
-        try:
-            name = af.read_entry()
-        except EOFError:
-            raise ValueError("data.tar not found")
+class ProcessingFinished(Exception):
+    pass
+
+class ImportpkgExtractor(DebExtractor):
+    def __init__(self, hash_functions, callback):
+        self.state = "start"
+        self.hash_functions = hash_functions
+        self.callback = callback
+
+    def handle_ar_member(self, name, filelike):
         if name.startswith(b"control.tar"):
-            if state != "start":
+            if self.state != "start":
                 raise ValueError("unexpected control.tar")
-            state = "control"
-            tf = decompress_tar(af, name[11:])
+            self.state = "control"
+            tf = decompress_tar(filelike, name[11:])
             for elem in tf:
                 if elem.name not in ("./control", "control"):
                     continue
-                if state != "control":
+                if self.state != "control":
                     raise ValueError("duplicate control file")
-                state = "control_file"
-                callback(process_control(tf.extractfile(elem).read()))
+                self.state = "control_file"
+                self.callback(process_control(tf.extractfile(elem).read()))
                 break
-            continue
         elif name.startswith(b"data.tar"):
-            if state != "control_file":
+            if self.state != "control_file":
                 raise ValueError("missing control file")
-            state = "data"
-            tf = decompress_tar(af, name[8:])
-            for name, size, hashes in get_tar_hashes(tf, hash_functions):
+            self.state = "data"
+            tf = decompress_tar(filelike, name[8:])
+            for name, size, hashes in get_tar_hashes(tf, self.hash_functions):
                 try:
                     name = name.decode("utf8")
                 except UnicodeDecodeError:
                     print("warning: skipping filename with encoding error")
                     continue # skip files with non-utf8 encoding for now
-                callback(dict(name=name, size=size, hashes=hashes))
-            break
+                self.callback(dict(name=name, size=size, hashes=hashes))
+            raise ProcessingFinished()
+
+    def handle_ar_end(self):
+        if self.state != "data":
+            raise ValueError("data.tar not found")
 
 def main():
     parser = optparse.OptionParser()
@@ -105,7 +108,12 @@ def main():
     dumper.open()
     if options.hash:
         stdin = HashedStream(stdin, hashlib.sha256())
-    process_package(stdin, hash_functions, dumper.represent)
+    try:
+        ImportpkgExtractor(hash_functions, dumper.represent).process(stdin)
+    except ProcessingFinished:
+        pass
+    else:
+        raise RuntimeError("unexpected termination of extractor")
     if options.hash:
         stdin.validate(options.hash)
     dumper.represent("commit")