Merge #16887: Abstract out some of the descriptor Span-parsing helpers

bb36372b8f2bd675313ae8553ceb61f28c2c1afd test: add unit tests for Span-parsing helpers (Sebastian Falbesoner)
5e69aeec3f2a0fafd5e591b7222716f00145761d Add documenting comments to spanparsing.h (Pieter Wuille)
230d43fdbc41b356700b0d8a6984d69e00279ade Abstract out some of the descriptor Span-parsing helpers (Pieter Wuille)

Pull request description:

  As suggested here: https://github.com/bitcoin/bitcoin/pull/16800#issuecomment-531605482.

  This moves the Span parsing functions out of the descriptor module, making them more easily usable for other parsers (in particular, in preparation for miniscript parsing).

ACKs for top commit:
  MarcoFalke:
    ACK bb36372b8f2bd675313ae8553ceb61f28c2c1afd

Tree-SHA512: b5c5c11a9bc3f0a1c2c4cfa22755654ecfb8d4b69da0dc1fb9f04e1556dc0f6ffd87ad153600963279ac465d587d7971b53d240ced802d12693682411ac73deb

1 files changed, 67 insertions, 0 deletions

diff --git a/src/util/spanparsing.cpp b/src/util/spanparsing.cpp
new file mode 100644
index 000000000..0c8575399
--- /dev/null
+++ b/src/util/spanparsing.cpp
@@ -0,0 +1,67 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <util/spanparsing.h>
+
+#include <span.h>
+
+#include <string>
+#include <vector>
+
+namespace spanparsing {
+
+bool Const(const std::string& str, Span<const char>& sp)
+{
+    if ((size_t)sp.size() >= str.size() && std::equal(str.begin(), str.end(), sp.begin())) {
+        sp = sp.subspan(str.size());
+        return true;
+    }
+    return false;
+}
+
+bool Func(const std::string& str, Span<const char>& sp)
+{
+    if ((size_t)sp.size() >= str.size() + 2 && sp[str.size()] == '(' && sp[sp.size() - 1] == ')' && std::equal(str.begin(), str.end(), sp.begin())) {
+        sp = sp.subspan(str.size() + 1, sp.size() - str.size() - 2);
+        return true;
+    }
+    return false;
+}
+
+Span<const char> Expr(Span<const char>& sp)
+{
+    int level = 0;
+    auto it = sp.begin();
+    while (it != sp.end()) {
+        if (*it == '(') {
+            ++level;
+        } else if (level && *it == ')') {
+            --level;
+        } else if (level == 0 && (*it == ')' || *it == ',')) {
+            break;
+        }
+        ++it;
+    }
+    Span<const char> ret = sp.first(it - sp.begin());
+    sp = sp.subspan(it - sp.begin());
+    return ret;
+}
+
+std::vector<Span<const char>> Split(const Span<const char>& sp, char sep)
+{
+    std::vector<Span<const char>> ret;
+    auto it = sp.begin();
+    auto start = it;
+    while (it != sp.end()) {
+        if (*it == sep) {
+            ret.emplace_back(start, it);
+            start = it + 1;
+        }
+        ++it;
+    }
+    ret.emplace_back(start, it);
+    return ret;
+}
+
+} // namespace spanparsing