Merge #15986: Add checksum to getdescriptorinfo

26d3fad1093dfc697048313be7a96c9adf723654 Add unmodified-but-with-checksum to getdescriptorinfo (Pieter Wuille)
104b3a5069c937383e6f88f2f3fb804ef61b208f Factor out checksum checking from descriptor parsing (Pieter Wuille)

Pull request description:

ACKs for top commit:
  achow101:
    Code Review ACK 26d3fad1093dfc697048313be7a96c9adf723654
  meshcollider:
    re-Code Review ACK 26d3fad1093dfc697048313be7a96c9adf723654
  Sjors:
    ACK 26d3fad1093dfc697048313be7a96c9adf723654

Tree-SHA512: b7a7f89b64a184927d6f9a0c183a087609983f0c5d5593f78e12db4714e930a4af655db9da4b0c407ea2e24d3b926cef6e1f2a15de502d0d1290a6e046826b99

2 files changed, 33 insertions, 10 deletions

diff --git a/src/script/descriptor.cpp b/src/script/descriptor.cpp
index 327af62a4f..d2b370b65d 100644
--- a/src/script/descriptor.cpp
+++ b/src/script/descriptor.cpp
@@ -914,27 +914,42 @@ std::unique_ptr<DescriptorImpl> InferScript(const CScript& script, ParseScriptCo
 
 } // namespace
 
-std::unique_ptr<Descriptor> Parse(const std::string& descriptor, FlatSigningProvider& out, bool require_checksum)
+/** Check a descriptor checksum, and update desc to be the checksum-less part. */
+bool CheckChecksum(Span<const char>& sp, bool require_checksum, std::string* out_checksum = nullptr)
 {
-    Span<const char> sp(descriptor.data(), descriptor.size());
-
-    // Checksum checks
     auto check_split = Split(sp, '#');
-    if (check_split.size() > 2) return nullptr; // Multiple '#' symbols
-    if (check_split.size() == 1 && require_checksum) return nullptr; // Missing checksum
+    if (check_split.size() > 2) return false; // Multiple '#' symbols
+    if (check_split.size() == 1 && require_checksum) return false; // Missing checksum
+    if (check_split.size() == 2) {
+        if (check_split[1].size() != 8) return false; // Unexpected length for checksum
+    }
+    auto checksum = DescriptorChecksum(check_split[0]);
+    if (checksum.empty()) return false; // Invalid characters in payload
     if (check_split.size() == 2) {
-        if (check_split[1].size() != 8) return nullptr; // Unexpected length for checksum
-        auto checksum = DescriptorChecksum(check_split[0]);
-        if (checksum.empty()) return nullptr; // Invalid characters in payload
-        if (!std::equal(checksum.begin(), checksum.end(), check_split[1].begin())) return nullptr; // Checksum mismatch
+        if (!std::equal(checksum.begin(), checksum.end(), check_split[1].begin())) return false; // Checksum mismatch
     }
+    if (out_checksum) *out_checksum = std::move(checksum);
     sp = check_split[0];
+    return true;
+}
 
+std::unique_ptr<Descriptor> Parse(const std::string& descriptor, FlatSigningProvider& out, bool require_checksum)
+{
+    Span<const char> sp(descriptor.data(), descriptor.size());
+    if (!CheckChecksum(sp, require_checksum)) return nullptr;
     auto ret = ParseScript(sp, ParseScriptContext::TOP, out);
     if (sp.size() == 0 && ret) return std::unique_ptr<Descriptor>(std::move(ret));
     return nullptr;
 }
 
+std::string GetDescriptorChecksum(const std::string& descriptor)
+{
+    std::string ret;
+    Span<const char> sp(descriptor.data(), descriptor.size());
+    if (!CheckChecksum(sp, false, &ret)) return "";
+    return ret;
+}
+
 std::unique_ptr<Descriptor> InferDescriptor(const CScript& script, const SigningProvider& provider)
 {
     return InferScript(script, ParseScriptContext::TOP, provider);
diff --git a/src/script/descriptor.h b/src/script/descriptor.h
index a34e9f0d8a..eae1e262cd 100644
--- a/src/script/descriptor.h
+++ b/src/script/descriptor.h
@@ -81,6 +81,14 @@ struct Descriptor {
  */
 std::unique_ptr<Descriptor> Parse(const std::string& descriptor, FlatSigningProvider& out, bool require_checksum = false);
 
+/** Get the checksum for a descriptor.
+ *
+ * If it already has one, and it is correct, return the checksum in the input.
+ * If it already has one that is wrong, return "".
+ * If it does not already have one, return the checksum that would need to be added.
+ */
+std::string GetDescriptorChecksum(const std::string& descriptor);
+
 /** Find a descriptor for the specified script, using information from provider where possible.
  *
  * A non-ranged descriptor which only generates the specified script will be returned in all