Add a build script which downloads the latest SQLite source

Recent SQLite source seems to be needed by gwenn/gosqlite, so this
script gets it all done.  This script is mostly just a copy of the
build script in the DBHub.io source code repo.

.gitignore

@@ -3,4 +3,6 @@ data/
 .idea
 config.toml
 db4s_cluster_downloader
-DB4S_downloads.sqlite
+DB4S_downloads.sqlite
+local
+other

build_db4s_downloader.sh

@@ -0,0 +1,47 @@
+#!/bin/sh
+
+# Useful variables
+DEST=${PWD}/local
+export PKG_CONFIG_PATH=${DEST}/lib/pkgconfig
+export GOBIN=${DEST}/bin
+
+# If this script is passed an argument of "clean", then delete the
+# locally compiled pieces
+if [ "$1" = "clean" ]; then
+  echo "Removing local SQLite and compiled DBHub.io executables"
+  rm -rf ${DEST} other/cache
+  exit
+fi
+
+# Builds a local SQLite
+if [ ! -e "${DEST}/lib/libsqlite3.so" ]; then
+  if [ ! -d "other/cache" ]; then
+    mkdir -p other/cache
+  fi
+  cd other/cache  || exit 1
+  if [ ! -f sqlite.tar.gz ]; then
+    echo "Downloading SQLite source code"
+    TARBALL=$(curl -s https://sqlite.org/download.html | awk '/<!--/,/-->/ {print}' | grep 'sqlite-autoconf' | cut -d ',' -f 3)
+    SHA3=$(curl -s https://sqlite.org/download.html | awk '/<!--/,/-->/ {print}' | grep 'sqlite-autoconf' | cut -d ',' -f 5)
+    curl -LsS -o sqlite.tar.gz https://sqlite.org/${TARBALL}
+    VERIFY=$(openssl dgst -sha3-256 sqlite.tar.gz | cut -d ' ' -f 2)
+    if [ "$SHA3" != "$VERIFY" ]; then exit 2 ; fi
+  fi
+  if [ ! -f sqlite.tar.gz ]; then
+    echo "Downloading the SQLite source code did not work"
+    exit 3
+  fi
+  echo "Compiling local SQLite"
+  tar xfz sqlite.tar.gz
+  cd sqlite-autoconf-* || exit 4
+  CPPFLAGS="-DSQLITE_ENABLE_COLUMN_METADATA=1 -DSQLITE_MAX_VARIABLE_NUMBER=250000 -DSQLITE_ENABLE_RTREE=1 -DSQLITE_ENABLE_GEOPOLY=1 -DSQLITE_ENABLE_FTS3=1 -DSQLITE_ENABLE_FTS3_PARENTHESIS=1 -DSQLITE_ENABLE_FTS5=1 -DSQLITE_ENABLE_STAT4=1 -DSQLITE_ENABLE_JSON1=1 -DSQLITE_SOUNDEX=1 -DSQLITE_ENABLE_MATH_FUNCTIONS=1 -DSQLITE_MAX_ATTACHED=125 -DSQLITE_ENABLE_MEMORY_MANAGEMENT=1 -DSQLITE_ENABLE_SNAPSHOT=1" ./configure --prefix=${DEST} --enable-dynamic-extensions=no
+  make -j "$(nproc)"
+  make install
+  cd ..
+  rm -rf sqlite-autoconf-*
+  cd ../..
+fi
+
+# Builds the Go binaries
+echo "Compiling DB4S downloader daemon"
+go install .