[wpiutil C++] Add remove_prefix() and remove_suffix()

glass/src/lib/native/cpp/support/DataLogReaderThread.cpp

@@ -96,25 +96,23 @@ void DataLogReaderThread::ReadMain() {
     if (data.empty()) {
       continue;
     }
-    if (wpi::starts_with(name, "NT:")) {
-      name = wpi::drop_front(name, 3);
+    if (auto strippedName = wpi::remove_prefix(name, "NT:")) {
+      name = *strippedName;
     }
-    if (wpi::starts_with(name, "/.schema/struct:")) {
-      auto typeStr = wpi::drop_front(name, 16);
+    if (auto typeStr = wpi::remove_prefix(name, "/.schema/struct:")) {
       std::string_view schema{reinterpret_cast<const char*>(data.data()),
                               data.size()};
       std::string err;
-      auto desc = m_structDb.Add(typeStr, schema, &err);
+      auto desc = m_structDb.Add(*typeStr, schema, &err);
       if (!desc) {
         wpi::print("could not decode struct '{}' schema '{}': {}\n", name,
                    schema, err);
       }
-    } else if (wpi::starts_with(name, "/.schema/proto:")) {
+    } else if (auto filename = wpi::remove_prefix(name, "/.schema/proto:")) {
       // protobuf descriptor handling
-      auto filename = wpi::drop_front(name, 15);
-      if (!m_protoDb.Add(filename, data)) {
+      if (!m_protoDb.Add(*filename, data)) {
         wpi::print("could not decode protobuf '{}' filename '{}'\n", name,
-                   filename);
+                   *filename);
       }
     }
   }

glass/src/libnt/native/cpp/NTField2D.cpp

@@ -126,7 +126,7 @@ void NTField2DModel::Update() {
   for (auto&& event : m_poller.ReadQueue()) {
     if (auto info = event.GetTopicInfo()) {
       // handle publish/unpublish
-      auto name = wpi::drop_front(info->name, m_path.size());
+      auto name = wpi::remove_prefix(info->name, m_path).value_or("");
       if (name.empty() || name[0] == '.') {
         continue;
       }
@@ -198,7 +198,9 @@ void NTField2DModel::ForEachFieldObject(
         func) {
   for (auto&& obj : m_objects) {
     if (obj->Exists()) {
-      func(*obj, wpi::drop_front(obj->GetName(), m_path.size()));
+      if (auto name = wpi::remove_prefix(obj->GetName(), m_path)) {
+        func(*obj, *name);
+      }
     }
   }
 }

glass/src/libnt/native/cpp/NTMechanism2D.cpp

@@ -256,7 +256,7 @@ NTMechanism2DModel::~NTMechanism2DModel() = default;
 void NTMechanism2DModel::Update() {
   for (auto&& event : m_poller.ReadQueue()) {
     if (auto info = event.GetTopicInfo()) {
-      auto name = wpi::drop_front(info->name, m_path.size());
+      auto name = wpi::remove_prefix(info->name, m_path).value_or("");
       if (name.empty() || name[0] == '.') {
         continue;
       }
@@ -307,7 +307,7 @@ void NTMechanism2DModel::Update() {
         }
       } else {
         auto fullName = nt::Topic{valueData->topic}.GetName();
-        auto name = wpi::drop_front(fullName, m_path.size());
+        auto name = wpi::remove_prefix(fullName, m_path).value_or("");
         if (name.empty() || name[0] == '.') {
           continue;
         }

glass/src/libnt/native/cpp/NetworkTables.cpp

@@ -727,11 +727,12 @@ void NetworkTablesModel::ValueSource::UpdateFromValue(
         mpack_reader_init_data(&r, value.GetRaw());
         UpdateMsgpackValueSource(model, this, r, name, value.last_change());
         mpack_reader_destroy(&r);
-      } else if (wpi::starts_with(typeStr, "struct:")) {
-        auto structName = wpi::drop_front(typeStr, 7);
-        bool isArray = structName.ends_with("[]");
+      } else if (auto structNameOpt = wpi::remove_prefix(typeStr, "struct:")) {
+        auto structName = *structNameOpt;
+        auto withoutArray = wpi::remove_suffix(structName, "[]");
+        bool isArray = withoutArray.has_value();
         if (isArray) {
-          structName = wpi::drop_back(structName, 2);
+          structName = *withoutArray;
         }
         auto desc = model.m_structDb.Find(structName);
         if (desc && desc->IsValid()) {
@@ -762,8 +763,8 @@ void NetworkTablesModel::ValueSource::UpdateFromValue(
         } else {
           valueChildren.clear();
         }
-      } else if (wpi::starts_with(typeStr, "proto:")) {
-        auto msg = model.m_protoDb.Find(wpi::drop_front(typeStr, 6));
+      } else if (auto filename = wpi::remove_prefix(typeStr, "proto:")) {
+        auto msg = model.m_protoDb.Find(*filename);
         if (msg) {
           msg->Clear();
           auto raw = value.GetRaw();
@@ -808,13 +809,15 @@ void NetworkTablesModel::Update() {
             m_server.publishers.clear();
           } else if (info->name == "$serversub") {
             m_server.subscribers.clear();
-          } else if (wpi::starts_with(info->name, "$clientpub$")) {
-            auto it = m_clients.find(wpi::drop_front(info->name, 11));
+          } else if (auto client =
+                         wpi::remove_prefix(info->name, "$clientpub$")) {
+            auto it = m_clients.find(*client);
             if (it != m_clients.end()) {
               it->second.publishers.clear();
             }
-          } else if (wpi::starts_with(info->name, "$clientsub$")) {
-            auto it = m_clients.find(wpi::drop_front(info->name, 11));
+          } else if (auto client =
+                         wpi::remove_prefix(info->name, "$clientsub$")) {
+            auto it = m_clients.find(*client);
             if (it != m_clients.end()) {
               it->second.subscribers.clear();
             }
@@ -854,27 +857,29 @@ void NetworkTablesModel::Update() {
             m_server.UpdatePublishers(entry->value.GetRaw());
           } else if (entry->info.name == "$serversub") {
             m_server.UpdateSubscribers(entry->value.GetRaw());
-          } else if (wpi::starts_with(entry->info.name, "$clientpub$")) {
-            auto it = m_clients.find(wpi::drop_front(entry->info.name, 11));
+          } else if (auto client =
+                         wpi::remove_prefix(entry->info.name, "$clientpub$")) {
+            auto it = m_clients.find(*client);
             if (it != m_clients.end()) {
               it->second.UpdatePublishers(entry->value.GetRaw());
             }
-          } else if (wpi::starts_with(entry->info.name, "$clientsub$")) {
-            auto it = m_clients.find(wpi::drop_front(entry->info.name, 11));
+          } else if (auto client =
+                         wpi::remove_prefix(entry->info.name, "$clientsub$")) {
+            auto it = m_clients.find(*client);
             if (it != m_clients.end()) {
               it->second.UpdateSubscribers(entry->value.GetRaw());
             }
           }
-        } else if (entry->value.IsRaw() &&
-                   wpi::starts_with(entry->info.name, "/.schema/struct:") &&
+        } else if (auto typeStr =
+                       wpi::remove_prefix(entry->info.name, "/.schema/struct:");
+                   entry->value.IsRaw() && typeStr &&
                    entry->info.type_str == "structschema") {
           // struct schema handling
-          auto typeStr = wpi::drop_front(entry->info.name, 16);
           std::string_view schema{
               reinterpret_cast<const char*>(entry->value.GetRaw().data()),
               entry->value.GetRaw().size()};
           std::string err;
-          auto desc = m_structDb.Add(typeStr, schema, &err);
+          auto desc = m_structDb.Add(*typeStr, schema, &err);
           if (!desc) {
             wpi::print("could not decode struct '{}' schema '{}': {}\n",
                        entry->info.name, schema, err);
@@ -884,25 +889,23 @@ void NetworkTablesModel::Update() {
               if (!entryPair.second) {
                 continue;
               }
-              std::string_view ts = entryPair.second->info.type_str;
-              if (!wpi::starts_with(ts, "struct:")) {
-                continue;
-              }
-              ts = wpi::drop_front(ts, 7);
-              if (ts == typeStr || (wpi::ends_with(ts, "[]") &&
-                                    wpi::drop_back(ts, 2) == typeStr)) {
-                entryPair.second->UpdateFromValue(*this);
+              if (auto ts = wpi::remove_prefix(entryPair.second->info.type_str,
+                                               "struct:")) {
+                if (*ts == *typeStr ||
+                    wpi::remove_suffix(*ts, "[]").value_or(*ts) == *typeStr) {
+                  entryPair.second->UpdateFromValue(*this);
+                }
               }
             }
           }
-        } else if (entry->value.IsRaw() &&
-                   wpi::starts_with(entry->info.name, "/.schema/proto:") &&
+        } else if (auto filename =
+                       wpi::remove_prefix(entry->info.name, "/.schema/proto:");
+                   entry->value.IsRaw() && filename &&
                    entry->info.type_str == "proto:FileDescriptorProto") {
           // protobuf descriptor handling
-          auto filename = wpi::drop_front(entry->info.name, 15);
-          if (!m_protoDb.Add(filename, entry->value.GetRaw())) {
+          if (!m_protoDb.Add(*filename, entry->value.GetRaw())) {
             wpi::print("could not decode protobuf '{}' filename '{}'\n",
-                       entry->info.name, filename);
+                       entry->info.name, *filename);
           } else {
             // loop over all protobuf entries and update (conservatively)
             for (auto&& entryPair : m_entries) {
@@ -1080,18 +1083,18 @@ void NetworkTablesModel::UpdateClients(std::span<const uint8_t> data) {
 }
 
 static bool GetHeadingTypeString(std::string_view* ts) {
-  if (wpi::starts_with(*ts, "proto:")) {
-    *ts = wpi::drop_front(*ts, 6);
+  if (auto withoutProto = wpi::remove_prefix(*ts, "proto:")) {
+    *ts = *withoutProto;
     auto lastdot = ts->rfind('.');
     if (lastdot != std::string_view::npos) {
       *ts = wpi::substr(*ts, lastdot + 1);
     }
-    if (wpi::starts_with(*ts, "Protobuf")) {
-      *ts = wpi::drop_front(*ts, 8);
+    if (auto withoutProtobuf = wpi::remove_prefix(*ts, "Protobuf")) {
+      *ts = *withoutProtobuf;
     }
     return true;
-  } else if (wpi::starts_with(*ts, "struct:")) {
-    *ts = wpi::drop_front(*ts, 7);
+  } else if (auto withoutStruct = wpi::remove_prefix(*ts, "struct:")) {
+    *ts = *withoutStruct;
     return true;
   }
   return false;

glass/src/libnt/native/cpp/NetworkTablesProvider.cpp

@@ -157,7 +157,8 @@ void NetworkTablesProvider::Update() {
       }
 
       auto topicName = nt::GetTopicName(valueData->topic);
-      auto tableName = wpi::drop_back(topicName, 6);
+      auto tableName =
+          wpi::remove_suffix(topicName, "/.type").value_or(topicName);
 
       GetOrCreateView(builderIt->second, nt::Topic{valueData->topic},
                       tableName);
@@ -196,9 +197,8 @@ void NetworkTablesProvider::Show(ViewEntry* entry, Window* window) {
   if (!window) {
     return;
   }
-  if (wpi::starts_with(entry->name, "/SmartDashboard/")) {
-    window->SetDefaultName(
-        fmt::format("{} (SmartDashboard)", wpi::drop_front(entry->name, 16)));
+  if (auto name = wpi::remove_prefix(entry->name, "/SmartDashboard/")) {
+    window->SetDefaultName(fmt::format("{} (SmartDashboard)", *name));
   }
   entry->window = window;
 

ntcore/src/main/native/cpp/LocalStorage.cpp

@@ -53,10 +53,11 @@ int LocalStorage::DataLoggerData::Start(TopicData* topic, int64_t time) {
   } else if (typeStr == "int[]") {
     typeStr = "int64[]";
   }
-  return log.Start(fmt::format("{}{}", logPrefix,
-                               wpi::drop_front(topic->name, prefix.size())),
-                   typeStr, DataLoggerEntry::MakeMetadata(topic->propertiesStr),
-                   time);
+  return log.Start(
+      fmt::format(
+          "{}{}", logPrefix,
+          wpi::remove_prefix(topic->name, prefix).value_or(topic->name)),
+      typeStr, DataLoggerEntry::MakeMetadata(topic->propertiesStr), time);
 }
 
 void LocalStorage::DataLoggerEntry::Append(const Value& v) {

ntcore/src/main/native/cpp/NetworkServer.cpp

@@ -224,8 +224,8 @@ void NetworkServer::ServerConnection4::ProcessWsUpgrade() {
   wpi::SmallString<128> nameBuf;
   std::string_view name;
   bool err = false;
-  if (wpi::starts_with(path, "/nt/")) {
-    name = wpi::UnescapeURI(wpi::drop_front(path, 4), nameBuf, &err);
+  if (auto uri = wpi::remove_prefix(path, "/nt/")) {
+    name = wpi::UnescapeURI(*uri, nameBuf, &err);
   }
   if (err || name.empty()) {
     INFO("invalid path '{}' (from {}), must match /nt/[clientId], closing",

ntcore/src/main/native/cpp/net/WireDecoder.cpp

@@ -567,7 +567,6 @@ bool nt::net::WireDecodeBinary(std::span<const uint8_t>* in, int64_t* outId,
   outValue->SetServerTime(time);
   outValue->SetTime(time == 0 ? 0 : time + localTimeOffset);
   // update input range
-  *in = wpi::drop_front(*in,
-                        in->size() - mpack_reader_remaining(&reader, nullptr));
+  *in = wpi::take_back(*in, mpack_reader_remaining(&reader, nullptr));
   return true;
 }

simulation/halsim_ws_server/src/main/native/cpp/HALSimHttpConnection.cpp

@@ -169,14 +169,13 @@ void HALSimHttpConnection::ProcessRequest() {
       !wpi::contains(path, "..") && !wpi::contains(path, "//")) {
     // convert to fs native representation
     fs::path nativePath;
-    if (wpi::starts_with(path, "/user/")) {
-      nativePath =
-          fs::path{m_server->GetWebrootSys()} /
-          fs::path{wpi::drop_front(path, 6), fs::path::format::generic_format};
+    if (auto userPath = wpi::remove_prefix(path, "/user/")) {
+      nativePath = fs::path{m_server->GetWebrootSys()} /
+                   fs::path{*userPath, fs::path::format::generic_format};
     } else {
       nativePath =
           fs::path{m_server->GetWebrootSys()} /
-          fs::path{wpi::drop_front(path, 1), fs::path::format::generic_format};
+          fs::path{wpi::drop_front(path), fs::path::format::generic_format};
     }
 
     if (fs::is_directory(nativePath)) {

wpiutil/src/main/native/thirdparty/llvm/cpp/llvm/StringExtras.cpp

@@ -278,7 +278,7 @@ bool wpi::detail::ConsumeSignedInteger(
   }
 
   // Get the positive part of the value.
-  std::string_view str2 = wpi::drop_front(str, 1);
+  std::string_view str2 = wpi::drop_front(str);
   if (wpi::detail::ConsumeUnsignedInteger(str2, radix, ullVal) ||
       // Reject values so large they'd overflow as negative signed, but allow
       // "-0".  This negates the unsigned so that the negative isn't undefined

wpiutil/src/main/native/thirdparty/llvm/include/wpi/StringExtras.h

@@ -357,6 +357,32 @@ inline bool contains_lower(std::string_view str, const char* other) noexcept {
   return find_lower(str, other) != std::string_view::npos;
 }
 
+/**
+ * Return an optional containing @p str but with @p prefix removed if the string
+ * starts with the prefix. If the string does not start with the prefix, return
+ * an empty optional.
+ */
+constexpr std::optional<std::string_view> remove_prefix(std::string_view str, std::string_view prefix) noexcept {
+  if (str.starts_with(prefix)) {
+    str.remove_prefix(prefix.size());
+    return str;
+  }
+  return std::nullopt;
+}
+
+/**
+ * Return an optional containing @p str but with @p suffix removed if the
+ * string ends with the suffix. If the string does not end with the suffix,
+ * return an empty optional.
+ */
+constexpr std::optional<std::string_view> remove_suffix(std::string_view str, std::string_view suffix) noexcept {
+  if (str.ends_with(suffix)) {
+    str.remove_suffix(suffix.size());
+    return str;
+  }
+  return std::nullopt;
+}
+
 /**
  * Return a string_view equal to @p str but with the first @p n elements
  * dropped.

wpiutil/src/test/native/cpp/StringExtrasTest.cpp

@@ -0,0 +1,35 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include <gtest/gtest.h>
+
+#include "wpi/StringExtras.h"
+
+TEST(StringExtrasTest, RemovePrefix) {
+  std::string_view original = "wpilib";
+  auto modified = wpi::remove_prefix(original, "wpi");
+  EXPECT_EQ(original, "wpilib");
+  EXPECT_EQ(modified, std::optional{"lib"});
+}
+
+TEST(StringExtrasTest, RemoveSuffix) {
+  std::string_view original = "wpilib";
+  auto modified = wpi::remove_suffix(original, "lib");
+  EXPECT_EQ(original, "wpilib");
+  EXPECT_EQ(modified, std::optional{"wpi"});
+}
+
+TEST(StringExtrasTest, RemovePrefixNoMatch) {
+  std::string_view original = "wpilib";
+  auto modified = wpi::remove_prefix(original, "foo");
+  EXPECT_EQ(original, "wpilib");
+  EXPECT_EQ(modified, std::nullopt);
+}
+
+TEST(StringExtrasTest, RemoveSuffixNoMatch) {
+  std::string_view original = "wpilib";
+  auto modified = wpi::remove_suffix(original, "foo");
+  EXPECT_EQ(original, "wpilib");
+  EXPECT_EQ(modified, std::nullopt);
+}