1 files changed, 93 insertions, 0 deletions
diff --git a/sigsum/ascii.py b/sigsum/ascii.py
new file mode 100644
index 0000000..f7f378c
--- /dev/null
+++ b/sigsum/ascii.py
@@ -0,0 +1,93 @@
+import io
+
+
+def dumps(data):
+    """
+    dumps takes a key/values mapping and serializes it to ASCII.
+    If one of the values is not of type str, int or bytes (or a list of those)
+    a TypeError is raised.
+    """
+    res = io.StringIO()
+    for key in data:
+        values = data[key]
+        if not isinstance(values, list):
+            values = [values]
+        for val in values:
+            if isinstance(val, (int, str)):
+                res.write(f"{key}={val}\n")
+            elif isinstance(val, bytes):
+                res.write(f"{key}={val.hex()}\n")
+            else:
+                raise TypeError(
+                    f"Object of type {type(val).__name__} is not ASCII serializable"
+                )
+    res.seek(0)
+    return res.read()
+
+
+def loads(txt):
+    """
+    loads deserialized the given string into an ASCIIValue.
+    """
+    kv = []
+    for lno, line in enumerate(txt.splitlines(), 1):
+        if "=" not in line:
+            raise ASCIIDecodeError("Expecting '=' delimiter line 1")
+        (key, val) = line.rstrip().split("=", 1)
+        if val == "":
+            raise ASCIIDecodeError("Expecting value after '=' line 1")
+        kv.append((key, val))
+    return ASCIIValue(kv)
+
+
+class ASCIIDecodeError(Exception):
+    """
+    ASCIIDecodeError indicates that loads couldn't deserialize the given input.
+    """
+
+
+class ASCIIValue:
+    """
+    ASCIIValue implements Mapping[str, List[str]] with convenience getters to
+    parse sigsum types.
+    """
+
+    def __init__(self, data):
+        self._d = {}
+        for k, v in data:
+            self._d.setdefault(k, []).append(v)
+
+    def __getitem__(self, k):
+        return self._d.__getitem__(k)
+
+    def __len__(self):
+        return self._d.__len__()
+
+    def __iter__(self):
+        return self._d.__iter__()
+
+    def getone(self, k):
+        v = self._d[k]
+        if len(v) > 1:
+            raise ValueError(f"{k}: expected a single value, got {len(v)}")
+        return self._d[k][0]
+
+    def getint(self, k, many=False):
+        if many:
+            return [int(x) for x in self._d[k]]
+        return int(self.getone(k))
+
+    def getbytes(self, k, many=False):
+        if many:
+            return [bytes.fromhex(x) for x in self._d[k]]
+        return bytes.fromhex(self.getone(k))
+
+    def __repr__(self):
+        return f'ASCIIValue([{", ".join(f"({k!r}, {v!r})" for k,vs in self._d.items() for v in vs)}])'
+
+    def __eq__(self, other):
+        if isinstance(other, ASCIIValue):
+            return self._d.__eq__(other._d)
+        if isinstance(other, dict):
+            return self._d.__eq__(other)
+        return NotImplemented