[asmap] Make DecodeAsmap() a utility function

DecopeAsmap is a pure utility function and doesn't have any
dependencies on addrman, so move it to util/asmap.

Reviewer hint: use:

`git diff --color-moved=dimmed-zebra --color-moved-ws=ignore-all-space`

src/util/asmap.cpp

@@ -2,10 +2,16 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <util/asmap.h>
+
+#include <clientversion.h>
+#include <crypto/common.h>
+#include <logging.h>
+#include <streams.h>
+
+#include <cassert>
 #include <map>
 #include <vector>
-#include <assert.h>
-#include <crypto/common.h>
 
 namespace {
 
@@ -183,3 +189,31 @@ bool SanityCheckASMap(const std::vector<bool>& asmap, int bits)
     }
     return false; // Reached EOF without RETURN instruction
 }
+
+std::vector<bool> DecodeAsmap(fs::path path)
+{
+    std::vector<bool> bits;
+    FILE *filestr = fsbridge::fopen(path, "rb");
+    CAutoFile file(filestr, SER_DISK, CLIENT_VERSION);
+    if (file.IsNull()) {
+        LogPrintf("Failed to open asmap file from disk\n");
+        return bits;
+    }
+    fseek(filestr, 0, SEEK_END);
+    int length = ftell(filestr);
+    LogPrintf("Opened asmap file %s (%d bytes) from disk\n", path, length);
+    fseek(filestr, 0, SEEK_SET);
+    uint8_t cur_byte;
+    for (int i = 0; i < length; ++i) {
+        file >> cur_byte;
+        for (int bit = 0; bit < 8; ++bit) {
+            bits.push_back((cur_byte >> bit) & 1);
+        }
+    }
+    if (!SanityCheckASMap(bits, 128)) {
+        LogPrintf("Sanity check of asmap file %s failed\n", path);
+        return {};
+    }
+    return bits;
+}
+

src/util/asmap.h

@@ -5,11 +5,16 @@
 #ifndef BITCOIN_UTIL_ASMAP_H
 #define BITCOIN_UTIL_ASMAP_H
 
-#include <stdint.h>
+#include <fs.h>
+
+#include <cstdint>
 #include <vector>
 
 uint32_t Interpret(const std::vector<bool> &asmap, const std::vector<bool> &ip);
 
 bool SanityCheckASMap(const std::vector<bool>& asmap, int bits);
 
+/** Read asmap from provided binary file */
+std::vector<bool> DecodeAsmap(fs::path path);
+
 #endif // BITCOIN_UTIL_ASMAP_H