Add header saving features

dotfiles/imapdomo/common.lua

     return false
 end
 
+function save_header(mesg, name)
+    --
+    -- Append header from *mesg* to file named *name*
+    --
+    -- File will be placed under directory specified by IMAPDOMO_HEADERS
+    -- environment variable.
+    --
+    local dest = os.getenv("IMAPDOMO_HEADERS") .. '/' .. name
+    local cmd = ('cat >>"%q"'):format(dest)
+    mbox, uid = table.unpack(mesg)
+    header = mbox[uid]:fetch_header()
+    if pipe_to(cmd, header) == 0 then
+        return true
+    else
+        return false
+    end
+end
+
+function filter_header_saved(seq, name)
+    --
+    -- Save headers from sequence
+    --
+    -- Append header of each message in sequence *seq* to file names
+    -- *name* and return new sequence with those messages where save was
+    -- successful.
+    --
+    result = Set {}
+    for _, mesg in ipairs(seq) do
+        if save_header(mesg, name) then
+            table.insert(result, mesg)
+        end
+    end
+    return result
+end
+
 function filter_part_like(query, seq)
     --
     -- Run MIME part query on *seq* sequence of messages

dotfiles/imapdomo/utils/imapdomo

     # Compose imapfilter command
     #
     echo -n "IMAPDOMO_ACTION=$Action"
+    echo -n "  IMAPDOMO_HEADERS=$HeaderDir"
     echo -n "  IMAPFILTER_HOME=$CfgDir"
     echo -n "  imapfilter"
     if $Debug
     local cmd       # imapfilter command
     local CfgDir    # config directory
     local LogDir    # directory to store logs
+    local HeaderDir # directory to store headers by save_header()
     local CdTo      # change dir to this before running imapfilter
     CfgDir="$HOME/.imapdomo"
     LogDir="$HOME/.local/share/imapdomo/logs"
+    HeaderDir="$HOME/.local/share/imapdomo/headers"
     Debug=false
     #shellcheck disable=SC2034
     while true; do case $1 in
     then
         cd "$CdTo" || die
     fi
+    mkdir -p "$HeaderDir" || die
     eval "$cmd"
 }
 

dotfiles/imapdomo/utils/imapdomo-cron

     # Compose imapfilter command
     #
     echo -n "IMAPDOMO_ACTION=$Action"
+    echo -n "  IMAPDOMO_HEADERS=$HeaderDir"
     echo -n "  IMAPFILTER_HOME=$CfgDir"
     echo -n "  imapfilter"
     if $Debug
     local cmd       # imapfilter command
     local CfgDir    # config directory
     local LogDir    # directory to store logs
+    local HeaderDir # directory to store headers by save_header()
     local CdTo      # change dir to this before running imapfilter
     CfgDir="$HOME/.imapdomo"
     LogDir="$HOME/.local/share/imapdomo/logs"
+    HeaderDir="$HOME/.local/share/imapdomo/headers"
     Debug=false
     #shellcheck disable=SC2034
     while true; do case $1 in
     then
         cd "$CdTo" || die
     fi
+    mkdir -p "$HeaderDir" || die
     eval "$cmd"
 }